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.
80:5 On Shabbos, it is forbidden to insulate a hot pot with any material, even one that doesn't intensify the heat. Therefore, one may not take a pot in which food was cooked or warmed and cover it with things like pillows or blankets to preserve its heat. (One may wrap a pot whose top is open as this is not truly insulating – Mishnah Brurah 253:69.)
80:6 Something that cannot be eaten without rinsing may not be rinsed on Shabbos, even with cold water. Salted fish like herring may be soaked in cold water because they could be eaten without rinsing them. (Mishnah Brurah 318:37 permits rinsing with cold water even if it is not otherwise edible.)