Our system of music notation is notoriously hard to learn - an arcane and ancient code invented by monks to help remember liturgical chants. It has been amended over the years to show things like rhythms, black notes, key changes, and dynamics; this has made it even more unintuitive and complicated.
For the frustrated garage guitarist, however, there is a simple alternative: tablature, or “tab.” Tab is based on the guitar’s fretboard; numbers tell the player on which strings and which frets to put their fingers. It’s no more sophisticated than playing Rock Band on the Wii.
I personally don’t like tab. It’s a terribly inefficient system: it takes a lot of space on the page, it doesn’t show rhythms, and it wouldn’t make sense for anyone other than a guitarist. No composer would write in tablature.
There is really only one reason for tab: you don’t have to have studied music to understand it. So if you’ve never had a lesson and you badly want to learn a particular song on your guitar, tab is the perfect thing. Some quick Googling and an hour or two of deciphering a tab chart, and any one of you can learn to play the “Sunshine of Your Love” riff in an afternoon. I dare you.