In an introductory note to this chapter, the Kitzur Shulchan Aruch writes that most Jews are already familiar with the prohibited labors of Shabbos and that he is only addressing common situations with which people may not be familiar. Clearly, the laws of Shabbos constitute an area requiring much greater study than this email alone will allow.
80:45 Normally, when a person needs to tie something with two strings, or when he wraps a cord around something and ties the ends together, he makes a double knot because one knot will not be secure. One may not, however, make a double knot on Shabbos, even if it is something that would normally be untied the same day. A person must be careful when he ties a kerchief around his neck on Shabbos that he does not make a double knot. Similarly, one must make sure on Friday that things he’ll wear don’t have any double knots because if they do, he will not be permitted to untie them on Shabbos. (In a case where it causes one distress, one may untie the double knot since this prohibition is rabbinic in nature and the rabbis did not institute the law to that great an extent – Rema 317:1) Also along these lines, one may not tie a knot at one end of a string or hold the ends together to make a knot on both ends because this kind of a single knot is also too permanent. To tie the two ends together with a single knot and a bow is permitted so long as one normally unties it within 24 hours. If not, then one may not do so on Shabbos even if his intention is to untie this particular knot the same day. To tie something with two or more bows is permitted, even if one intends to leave it tied for many days.
80:46 A knot that one may not tie on Shabbos, one may likewise not untie on Shabbos. If it creates great difficulty, one may have a non-Jew untie it.