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.
80:63 Just we may not write on Shabbos, so too may we not erase what has already been written. One is permitted to break and eat cakes that have letters or pictures on them. (Rema 340:3 disagrees. Mishnah Brurah 340:15 only objects when the writing is made of a different item, such as icing on cake; there is no problem, he says, when the cake itself is baked in the shape of letters.)
80:64 There is a difference of opinion when it comes to books that have letters written along the edge of their pages, with some authorities permitting these books to be opened and closed on Shabbos and others prohibiting it. The Kitzur Shulchan Aruch recommends avoiding the problem altogether by not writing along the edges of books in this manner. (Even though some authorities permit this, it would still be better to use another copy of the book if one is available – Mishnah Brurah 340:17.)