Hammer ons and pulloffs mean that you don't pick each note, but either just hit the notes, or pull off a finger so that the other finger, that is left on a lower fret will ring.
Like:
E---5--3---
B------(p)---
If that was a pull off from 5 to 3, you'd pick the 5, and then pull your finger off the 5th fret, and leave your finger on the 3rd fret, so it'll keep ringing.
Here's more:
http://www.cyberfret.com/techniques/hammer-ons-pull-offs/index.php
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