An eighth note 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.
Once you are confident counting triplets, try playing through a bar of eighth notes followed by a bar of eighth note triplets while playing the bass drum on 1 2 3 4 to keep steady time.
The following beat uses triplets, played by the right hand. Once again, remember to keep the notes even and the sound consistent.