When is ש pronounced as "s" and when is it pronounced as "sh"?
If there's nikkud you can tell by a dot on the upper left side (s) or upper right side (sh) of the letter. Without nikkud there's no way to tell, you just have to remember.
hee shotah khaláv
Why does "drinking" have a niqqud? I thought this course didn't use them.
You don't have to use it, the checker accepts the answer without nikkud. The reason they added it here is to make sure you understand the difference between masculine and feminine conjugation of שותה (shota - feminine, shote - masculine).