iTunes will not just magically tag your tracks, although it is good if you are looking for something that is going to be pretty userfriendly as far as conversions go. It's kind of a program for people who would rather just like some software handle it than do it themselves.
If you have tracks that are mislabeled, etc...but you actually know what they are, I'd suggest visiting musicbrainz.org and downloading the tagger. It takes a bit to figure it out, but it's a very nice tagger. It will change the file names for you, so if iTunes gives you hell about certain track orders (which is does on occasion), you can tag the tracks really well.