This exercise is from the Core Skills section on the Hammer on Pull off combination.

A hammer on / pull off combination is simply what the name suggests - you hammer on to a note, then, pull off that note again. The difference is that it is all done in one fluid action. It is often used for speed, but not always. You'll find it is one of the most common techniques on guitar, so will need to know it.

It is simple in ActionTabs - a standard coloured finger dot, with an H inside, quickly followed by a P. Of course, the pull off means that you remove your finger from the string, so the dot will disappear straight afterwards.

Listen to the technique and get familiar with its sound. You'll find that many songs use it. Here's a simple example from the introduction video to try out.

Remember that it is one single finger movement which can be broken down into 2 parts (H + P). It is often easier to play it by thinking of it in this way, than by separating it into its parts and playing them one-by-one.

Don't be put off if you find it uncomfortable and awkward at first. Every guitarist must build up finger technique and strength gradually through practice, patience and sore fingers. This technique should be easier the higher up the strings you apply it.