Guitar tablature is a system of notation that graphically represents strings and frets of the guitar fretboard. Each note is indicated by placing a number which indicates the fret to play, on the appropriate string. Now, I know a lot of people get confused on which string each line represents, and it makes sense because it's shown in reverse - the thickest string being the bottom most line and the thinnest string being the topmost.If you look at the diagram below, it would be played with the finger behind the 1st fret on the 5th string.

The numbers system is very easy to learn and understand. If it is 0, then you play the open string. If it is a number greater than 0, you need to press your finger on that fret number when you play. Remember that 1 is the closest fret to the stock, and the numbers going up as they get closer to the body. If you want to see more, check out this YouTube tutorial for beginners:

The tablature contains additional symbols that their purpose is to tell you how you should play the note. You have to pay attention to those notes if you want to play it correctly, otherwise your guitar playing will sound "dry"...

'h' - Hammer on.
It's picking a note and then hammering done with the fretting hand on the second note. The second note kind of echos the first one (3^5). It looks like this on the tablature:

'b' - String bends.
The fretting hand bends the string and gives it a wobbly effect. Looks like this:

'/' and '\' - Slides.
There are two types of slides - up and down. Slide up means you play the first note and then slide the finger that is holding that note up to a higher note. Slide down means you play the first note and then slide the finger that is holding that note down to a lower note.

'v' - Vibrato.
It's bending the string up and down quickly to create a moving sound. Looks like this :