There are 2 types of clef. The clef you will see on your music depends on what instrument you play. On guitar you will see music written on a Treble Clef - on bass guitar it will be on a Bass Clef.
Treble Clef:

Bass Clef:

Now you may be wondering why there are 2 different clefs. This is so that the notes that are in the lower range can be written seperately so as not to confuse the player. You see some notes will appear so far down that it would be confusing to read.

Below are the the names of the notes for both clefs.

Although on guitar or bass you probably only need to one or the other it is good to know both from a compositional point of view.

The Treble Clef:

The Bass Clef: