Alright Ive just started my programming education on university and the last lecture was about the different programming languages.

One thing that puzzled me was about the group called "Functional languages" (Lisp for example), our teacher said it uses mathematical expressions and functions, and nothing more.
It made me think...doesnt that make such languages pretty useless? I mean what can you do with them? Can you even write to / read from files? Not trying to bash the "Functional Languages", Im just curious...what are the advantages and where are they used?