Slap and Pop are one of the tequniques that define Bass. If any of you have 
not learnt slap, you can read my advice here. Using your thumb, hit the string 
downwards so your thumb is horizontaly across the strings. When slapping, 
be sure to slap the string with the bone protruding from the edge of your thumb, 
and very quickly take your thumb away to make this twangy noise. Here are 
some things to Help
Slap on E string:
G————————————————
D————————————————
A————————————————
E—0—0———0——0—0———
This is the easiest string to slap on.
Then we have pop. Pop is when you pull up the string and it also makes a sharp, 
twangy sound. If you want a good Slap/Pop riff then I advise the Red Hot Chili 
Peppers' Higher ground. Take it slowly at first. It may seem hard at first, 
but with  months of practice you will sound like a pro.