I know Judaism puts an emphasis on clean speech. What are the speech laws in Judaism and what do they mean? Thank you.

As always, there are many details involved which should be studied seriously and enthusiastically, but in the short scope of this framework, there are basically 3 major topics of clean or proper "speech": 1. Not to lie, slander or gossip about others. 2. Nevertheless, when it's necessary for the good and protection of society or the individual, not only is it allowed, but it's a mitzvah to publicize. Such proper speech should be used for positive purposes, such as education, idealism, truth, and morality, helping and making others feel good. 3. Not to use "dirty" words as accepted among the refined and well-mannered of each society. Rav Ari Shvat (Chwat)