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.
80:37 A person who is traveling on Shabbos in order to perform a mitzvah, such as to greet his father or his teacher, may cross through a stream so long as he does so in an unusual fashion (though it would be better to walk around it, if possible – Mishnah Brurah 301:12). An example of an usual fashion would be keeping his hands in his pockets so that he’ll remember not to wring the water out of his clothes. He may not cross the stream wearing sandals because they can't be tied tightly so we are concerned that they might fall off and he will come to carry them; he may, however, cross the stream wearing shoes. Since he is traveling for the sake of a mitzvah, he may also cross the stream on his way back. If a person travels in order to guard his produce, which has an aspect of a mitzvah to it, he may cross the stream on his way there but not on the way back.
80:38 If a person has mud on his clothes, if it's still wet, he may scrape it off with his fingernails or with a knife. If it has dried, he may not scrape it off because it resembles the melacha of tochein (grinding). (It’s possible that one might ask a non-Jew to remove it - see Mishnah Brurah 302:36 for details.)