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.
80:51 If a container has a cloth wrapped around its opening, tied closed with a string, one may tear the wrapping (or cut it with a knife – Mishnah Brurah 314:31) in order to open the item on Shabbos. This is allowed because it is a destructive act, and such acts are permitted for Shabbos needs. (Bi’ur Halacha 314:1 s.v. asur points out that destructive acts are not typically permitted for Shabbos needs.)
80:52 We are not permitted to trap any living creature on Shabbos, not even an insect. However, if the insect is on a person and biting him, he may take it and discard it because of the discomfort it is causing him. (Some permit one to discard it preemptively, before it starts biting him. In any event, shaking the insect off is preferable to carrying it out – Mishnah Brurah 316:37.) One may not kill the insect because we are not permitted to kill any living thing on Shabbos. There is a tradition that one may kill head lice on Shabbos, but this does not apply to other species of lice. (If one isn’t sure what kind of louse it is, he may capture it but not kill it – MB 316:36.)