One who twists fibers together to form a rope transgresses the prohibition of Kosheir, and one who pulls apart the strands of a rope transgresses Matir (MT 10:8).
One may not string pearls on Shabbat, because one may come to tie a knot at the end of the string. Similarly, if a pearl necklace snaps, one should not restring the pearls, because one may come to tie the string in a knot (MB 317:20). However, children may string beads that come in children’s craft sets and are not meant to last, since the knots of such necklaces are not permanent (SSK 16:22).
Some maintain that one may not insert shoelaces into new shoes because this makes the shoe wearable, thus transgressing the prohibition of fixing a kli (Ketzot Ha-shulĥan §146, Badei Ha-shulĥan §3). Others maintain that one may not insert new laces even into old shoes (MB 317:18; SSK 15:64). Still others maintain that nowadays one may insert laces into new shoes, because the eyelets in modern shoes are wide, so inserting shoelaces in is easy and is not considered a melakha (Yabi’a Omer 9:108:162). In order to comply with all the positions, it is proper to insert the laces in an unusual way. For example, one can either skip some of the eyelets or lace only the top ones. This will ensure that on Saturday night he will need to re-lace the shoes in the normal way and therefore has not fixed a kli on Shabbat (SSK 15:64).
One may thread a belt through the belt loops of a new pair of pants, since the belt is not meant to remain there forever. Similarly, one may insert a pillow into a pillowcase. However, one may not insert a tie or strap into a new dress or pair of pants if it is meant to remain there permanently, because doing so is fixing the item of clothing by making it wearable (MB 317:16; SSK 15:66).