Ipod/Itunes Question

Good day all. Apologies if this in the wrong forum.

My daughter go an Ipod for Christmas. I have no clue about these things (still using a portable cd player) .
Are we stuck with Itunes or can we use othe types of audio files on the Ipod? If we can use other files and they need to be converted, what is a good cheap/free conversion program? Thanks!

Golferguy