Watch the Working With Tablature (Tab) online guitar lesson by Rich Maloof from Acoustic Guitar For Beginners
Like any web search through user-generated material, finding good song tabs online is a treasure hunt. There's a lot of dirt to dig through, some fool's gold, and some really valuable finds.
Tab, or tablature, is actually a system of lines and numbers representing notes on the guitar neck. But in the digital age, "tab" has become a catch-all term for home-grown music charts. Users post their own shorthand versions of sheet music, making for a huge huge variety of forms and styles available online. It becomes even more of a musical mindfield when people show chords they THINK they hear without knowing for sure how a song should be played.
So, the Internet can be a great source but you have to be wary. For now, stick to those tabs that show just chords and lyrics. Try the chords shown against the original recording and see if it sounds close. Even if the chords are right, there is rarely any representation of bar lines, so you'll want to count your way through the tune once or twice to get your chords lined up with the lyrics.