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.
80:11 Regarding legumes and similar such things in their pods, if the pods are still soft and fit to be eaten, one may open them and remove the peas on Shabbos.This is permitted because it is considered removing food from food. If the pods have dried so that they are no longer edible, we may not remove the peas on Shabbos. (Some permit this to be done in an unusual fashion - see OC 319:6 and Rema there.) Similarly, we may not remove walnuts from their green outer shells or sesame seeds from their shells. (It is permitted to break the hard shell and the thin membrane of walnuts - Mishnah Brurah 319:24.)
80:12 We may not squeeze fruit in order to extract juice on Shabbos. Accordingly, we may not squeeze lemons into water to make lemonade. (One may squeeze a lemon onto food, including sugar, which may then be stirred into a liquid - MB 320:22.) According to some authorities, we may not even suck the juice straight from a fruit. We certainly must be careful with grapes (and olives - MB 320:12) that we don't suck the juice and discard the skins. However, if one doesn't need the juice, it is permitted to squeeze produce. We are therefore permitted to squeeze things like lettuce and cucumbers whose juice is discarded.