I haven't long to try and answer, but there are others with more expieriance and time to give a better answer, so this might get you started.
You already know the chords, and the strings.
Going from the top of the guitar to the bottom;
However, you'll notice that alot of times when someon posts TABs it will read;
As long as you know the strings it shouldn't matter too much, it does sometimes confuse though. Take it slow.
The 'X' represents a string that isn't played and an'0' represents an open string. The same so far.
Now to read a Tab: The number represents the Fret and the letter represents the string. Ex... 7G... This means that you only play the G string on the 7th Fret. If It shows 5D, Then it means to play only the d string on the 5th Fret. Find the Fret whether it's the 5th, 7th, 14th, or whatever, then look to see what's being played and play what is being shown. If you get a TAB that shows something like...XX0232...that means you don't play the E or B, you'll hold down on the D string second Fret, the A string on the third Fret and the e string on the second Fret. Does this look familiar.
Tabs are a single number, or it could appear as a group of numbers. Then you'll have some songs that will post a chord, but will say to play a single string.
If I've confused you, I'm sorry.
If I rambled a bit then I'll go ahead and appologize for that to.