I'm actually posting a video this Saturday about this topic, watch this space
But yes your basically right:
A pull off is when you play a note, then while sustaining the note drag the fretting finger down and off the string, basically plucking the string with that finger playing the note below on the same string.
While a Hammer on is the opposite where after playing your initial note and keeping it sustained, you "hammer down" another finger on the same string at a higher fret.
I play a: Jackson/Charvel Model 6
Through a: Marshall TSL100, Roland JC-120, ZenDrive
I make guitar tutorials and reviews here:
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