The magician shows an empty tube, closed fist, mouth, or other container, reaches inside, and produces an incredibly long multicolored streamer or chain of tied-together silks.
Let's look at the production of streamers from an "empty" tube first. There is a bit of psychology involved in the performance of this trick, in that spectators tend to concentrate on the hole at the end of the tube from which the magician is producing things and completely forget that there is a hole a the other end of the tube as well. To produce a long streamer, the magician simply reaches into the tube far enough that his hand extends out the "forgotten" hole and into his sleeve where the end of the streamer has been hidden. The streamer actually runs up the magician's sleeve and then beneath his clothes, down through the pants to either a reservoir beneath the stage or a large bucket behind the magic table filled with streamer. The streamer is then pulled from the tube until its length (or the magician) is exhausted.
Production of a streamer from the fist is even more simple, as the fist is so much closer to the sleeve. The magician just reaches a finger through the fist to grab the edge of the streamer and proceeds as described above.
Production of a streamer from the mouth is more difficult as it requires the swallowing of great lengths of streamer, and if the magician accidentally swallows both ends (instead of leaving one in the mouth), a second streamer must be swallowed. This takes a great deal of practice and, unfortunately, can lead to sudden bowel obstruction and painful death and/or fatal choking, which is why most magicians preferred to produce streamers from the mouth of a specially trained rabbit until those fun-stoppers at the SPCA put an end to that.
Producing tied-together silks is much the same as producing a streamer, but has the advantage of being more compact. Silks are laid carefully in a pile and hidden in the magician's sleeve. They are then knotted together one at a time with left hand using a one-fingered half-shank corner tie (familiar to Boy Scouts and sailors) while the right hand pulls them from the tube (or whatever).