I am new to the topic, so I'm trying to get an overview. I am aware of the relation between modular forms and $L$-series (but don't know what that does) and FLT.

Are there other applications of modular forms other than counting problems (by obtaining the coefficients of a series) in number theory?

A short list would be sufficient but a little more detail with that would be helpful.

EDIT:
I am aware of **this post** but my question is specifically on number theory.