A triplet is a group of three evenly spaced notes played within one beat. Eighth note triplets are indicated by three eighth notes grouped together by a bracket (or a curved line) and the numeral 3.
The eighth note triplets are played with one third of a beat each. Triplets are easy to understand once you have heard them played. Triplets are easy to understand once have a feel for how they are played.
The following 12 Bar Blues demonstrates the use of triplets. As with any new rhythm you learn, count as you play and tap your foot on the beat to help you keep time.