12 Bar Blues is a pattern of chords which repeats every 12 bars. There are hundreds of well known songs based on this chord progression, i.e., they contain basically the same chords in the same order. 12 Bar Blues is commonly used in Rock music. Some well known songs which use this 12 bar chord pattern are:
Play the following 12 Bar Blues, in the key of C major, which uses the C, F, and G chords you have learned so far. When a song is said to be in the key of C major, it means that the most important chord (and usually the first chord) is the C chord, and that the notes of the melody of the song are from the C major scale. This pattern of chords will probably sound familiar to you.