Ordinarily you promote to a queen by default, with only two main exceptions of which I can recall: (1) A queen is too much force that forces a stalemate; (2) A knight has the motion you need to win. Both of these cases are rare. I recall one thread mentioned another case of required underpromotion to a bishop, but I didn't read the details.
Here's an example of case (2) where Black gets permanently ahead in material by using underpromotion to a knight:
Source:
Palatnik, Sam, and Lev Alburt. 2013. Chess Tactics for the Tournament Player. New York, NY: Chess Information & Research Center. Page 180.
Hello, I have a question, when do you minorpromote pawns (with other words: when do you mor