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.
80:21 One may only cut onions and other vegetables on Shabbos immediately before the meal. Even then, we may not cut them very fine.
80:22 We may not salt anything that the salt will soften or make less pungent because this is similar to tanning leather. Therefore, one may not salt cucumbers, radishes, or onions even for the same meal. He may, however, dip each individual piece into salt as he eats them. Something like eggs and cooked meat, where the salt only imparts flavor, may be salted for the same meal but one may not salt them in advance for a later meal.