What's the best/easiest to use batch tagger ?

[Ton]

I already did some searching but this id3 tagging is still rather confusing for me. I find a lot of technical terms that I still don't understand.
I have a number of mp3 files where the id 3 info is missing, incomplete or wrong, so that they don't show up (right)in the Media Library. So I would like to correct this with as little work/typing as possible. I think to have understood that I need a batch tagging tool. Am I right ?
If so, what would be the best and/or easiest tool for this purpose ? (Preferrably but not necessary free).