It's not too hard. With tabs, you don't worry about the rhythm (you should have a feel for how the song goes). Here is a simple tab, and I will explain it.
e------2--------------------------2-----
B------------3------------0-------------
G-------------------2-------------------
D----------------------------------------
A----------------------------------------
E----------------------------------------
Now, you can see how the strings are laid out much like your very own guitar (assuming you have a standard tuning). The Number on the string tells you which fret to push your finger down on. For this tab, I would first play the second fret on the e string. Next, I would play the third fret on the B string. For the rhythm, like I said, you have to know the song. Lets assume this riff has a nice, syncopated rhythm. Ba-ba Ba-ba. A dotted quarter note and an eighth note.
The placement of your fingers will be, in this case, in the position of a D Chord. When the "0" is played, remove your ring finger form the B string. This way, you won't be moving only one finger to all the strings, but rather, using all of them for comfort. The finger positioning, obviously, depends on the song.
I hope this simple explanation is enough to get you started.