This exercise is from the Core Skill section on Hammers.

If you listen to the Normal Speed version you will hear how hammers like in this exercise can be used to play fast. This is because hammers can be performed in rapid succession and the picking hand isn't so involved.

Here we pick the open high E string, then instantly hammer on the G (3rd fret) with the 1st finger, instantly followed again by a hammer on the A (5th fret) using the 3rd finger. Without any pauses, instantly pick the open high E string again and repeat.

This is a 'triplet' - 3 notes played quickly together (in the same time as 1 normal note), then repeated. Some people mentally count '1-2-3' to a regular rhythm in their heads as they play each note, then speed up as they get more practiced. The point of learning that way is to avoid any gaps appearing between notes, yet keeping each note duration accurate. Of course, just practicing along with the ActionTab looped will also help too!

The 3 notes in this triplet are: E - G - A from the E minor pentatonic scale. This is a very typical fast triplet that is used a lot in blues and rock solos. It's also not so difficult to do with practice. It sounds good, it's fast, it will help you ROCK!