Originally Posted by: ThraxionThe arch looking rainbow thingy inbetween two numbers on tab is hammer on right?

If so how do you hammer on 0?

In my tab book it has 4 arch thingy then 0 then arch thingy then 7 (4h0h7)

You must be trying to learn "Thunderstruck" by AC/DC.
The arch is grouping the notes for a hammer-on and pull-off technique to get all of the notes producing sound. Thunderstruck's riff is intended to be played without picking a note, just using hammer-ons. The tab should sound as follows:
h4p0h7p0=x4 (x4 = do it 4 times), h5p0h8p0=x4, etc.
After all that "you've been Thunderstruck"
Hope that helps.