There have been archaeological finds of fingerloop braids from as early as the 12th century, and documented patterns - written pattern books - dating from the 15th century. Most of the surviving braids are done in silk thread, and many seem to be monochrome (though that may be a matter of the dyes fading to nothing over the years).
Fingerloop braiding is done by making loops of thread, then manipulating them variously - passing loops through loops in different patterns - to form braids. A braid's length is set before the braiding begins - a strand of thread is cut and doubled to form a fixed-length loop and the braid cannot be extended. Also, the upper limit of length for a braid is generally set by the width of the braider's reach, because the loops need to be pulled firmly apart to tighten the braid after each manipulation. However, this limit can be overcome by arranging a device to tap down the braid, or by getting an assistant to tighten the braid while it's out of the braider's reach.
Measure out the length of thread you want - you need twice the length of the finished piece, plus about 6 inches for the knot at the beginning and the unbraidable loops at the end, plus about a third of the finished length for take-up (multiply the finished length by 1.2 or 1-1/3 (larger numbers for thicker threads), add 6 inches, and double it). You can do fingerloop braiding with as few as three loops; the kits use five and eight. Eight is as many loops as one person can handle. There are patterns for 12-and 16-loop braids, worked by several people at once.
There are two kits; one uses five loops - two white, three colored - and the other uses eight - four each white and colored. You'll learn to work three different braids on the five-loop kit - a round (square) one, two thin braids at once, and a flat lace. The eight-loop kit makes a totally different braid, a spiral. You will find the patterns I teach in nearly every listing of fingerloop braid patterns.
When you've measured and cut your threads, you need to fasten them in a loop. First run your fingers along and through the threads so they're reasonably untangled and stretched the same; lay the ends together, give the newly-formed loops a pull just to make sure they're the same length, then tie the ends into an overhand knot. Note that the first few exchanges will be a little muddled, before the loops get straightened out; when you're finished, you can reknot a little higher and cut off the muddled bit if you think it looks bad.
Fasten the knotted end to something, then put each loop on one finger. Your fingers are labeled A (index), B (middle), C (ring), and D (pinkie) on each hand. For five loops (or bowes, as you'll often see them called), you'll put loops on B and C on one hand and on A, B and C on the other. Put the loops at your first knuckle, and crook your fingers a little to hold them. Back up until the threads are stretched out firmly but not tautly between your hands and the fastening. Now you can begin to braid.
Most of the patterns you'll find for fingerloop braids are taken directly from 15th and 16th century pattern books, and the language shows it.
Translated:
A round braid of 5 loops, for one person.
Put three loops on your left hand, on A, B, and C (index, middle, and ring fingers); put two on your right hand, on B and C (middle and ring fingers).
With A R(ight) (the finger that doesn't have a loop), reach through the two loops on that hand on B and C and pick up the bottom loop on the left hand; pick up the bottom strand of the loop (that's reversed). Pull it back through B and C and put it firmly on A R.
Move the loops on the left hand down; the one that was on B goes down to C, the one that was on A goes down to B. Now you've reversed the pattern - you have three loops on your right hand and two on your left.
With the unoccupied finger (A L), reach through B and C on that hand to pick up C on the right hand (from the bottom). You may have to use your thumb to help get the loop through the others, on one hand or the other.
Move the loops down on the right hand, and do it again.
This makes a round (actually squarish) braid with alternate diagonals of each color, as above.
The thing they don't mention in the pattern is that each time you change a loop from one hand to the other, you need to pull the braid apart as wide as you can - spread your hands - so that the braid is smooth and firm. Sometimes you want a softer braid, but generally you'll want to pull pretty firmly. This is also the point at which another person can tap down the braid for you by putting a finger between the two handfuls of loops and pressing lightly on the junction.
This braid is interesting because the manipulation is almost identical to the round braid above, but you get two thin braids at once! You can use these two braids to make a cord with slits in it for fastening things through. The only difference in the instructions is that for this braid, instead of taking the bottom strand of the bottom loop each time, you will take the same loop by the top strand (so it doesn't flip over as it changes hands).
Loops on ABC L and BC R.
A R reach through BC R and pick up C L by the top strand. Put it on A R.
Move the loops on your left hand down one.
A L reach through BC L, pick up C R by the top strand.
Move the loops on R down; repeat until done.
Again, the manipulation is almost the same as the above two. In fact, it has two variation to match the two above, but there's almost no visible difference so it's not really worth separating them. In this braid, instead of reaching through the two loops, you reach between them, and pick up the lowest loop on the other hand by either the top or bottom thread (I think top looks slightly better, but it's a minuscule difference). The end result is a nice flat braid (much better for sewing on as trim, for instance), with a sort of spiral-ish pattern.
Loops on ABC L and BC R.
A R reach between BC R and pick up C L by the top strand. Put it on A R.
Move the loops on your left hand down one.
A L reach between BC L, pick up C R by the top strand.
Move the loops on R down; repeat until done.
This braid uses 8 loops, filling both hands. It produces a lovely spiral, like a twined cord but much stronger.
Put four loops of one color on ABCD R
Put four loops of a different color on ABCD L
Do an exchange, A R with D L. That is, take the loop on A (index) R and put it on D (pinkie) L; pick up the loop on D L and put it on A R. The best way to do this is to put all the loops into the bend of your top knuckle (closest to the fingertip); bend your fingers to hold the loop on. Stick your right index finger through the loop on your left pinkie, and hook that loop off at the second knuckle of your index finger. Then use the (now unoccupied) pinkie to take the front loop off the right index finger. Exchange done.
Now exchange B R with C L
C R with B L
D R with A L
Tighten after each exchange.
When you've gone up one hand and down the other (4 double exchanges), start over with A R to D L.
These are only a few examples - there are literally hundreds of fingerloop braiding patterns. Many are available on the Web - see the links section below.
When you've braided the length you want, or when the loops get too small for easy manipulation, it's time to finish off - which is very simple. Pull your fingers out of the loops and tie an overhand knot as close to the braided area as you can manage. Cut off the excess loops, and you have a finished braid. The 8-loop and basic 5-loop above make excellent purse strings or drawstrings for bags or clothes; 5-loop variation 1 can be used to make eyelets or places to tie off a string; 5-loop variation 2, among others, makes flat braids that can be sewn onto clothing like lace or used as straps. Investigate on the Web or in your local library to find some of the many other patterns available.
Old English Pattern Books for Loop Braiding by Noemi Speiser. Patterns and instructions for many different braids.
"Fingerloop braiding: The makyng of a lace of bows" by Lady Sylvie la Chardonnière (class handout)
Fingerloop.org - Good, thorough information about braiding - historical patterns, archaeological finds, other sources. Main page is general information and links to other sites; this page has links to patterns and pictures of many different braids.
The Tudor Costume Page/Braids - clear pictures and diagrams for a simple and a complex braid, including pictures of how to do the exchange for the eight-loop braid.
Phiala's String Page/Braiding - Fingerloop Braids. Patterns for several 5-loop braids, plus some information on braiding with more than one person.
ThirteenthCentury.com - a very clear set of diagrams showing reaching through one loop to pick up another from the other hand (click the 'next' link at the upper right), plus some archaelogical information.