The wiki how answer is very good.  Once you think you know how to read and understand guitar tablature, then a very good site to find thousands of songs you know and like is ultimateguitar.com  The site is free, albeit with pop ups and such, but it has a wealth of information and songs from every genre.  To get around copywrite issues alot of the music only has partial lyrics, but you can get those from other sites.  I have been playing for 40 years and if I had had all the access to information and the internet when I was a kid learning to play, I might famous now.