Every gang is at least slightly different in what they call each other rank-wise. It's basically like a military system almost. One common position would be a "shot-caller" which would be the highest ranking person in your clique, but that "shot-caller" would report to a, say, block or 'hood "shot-caller", who reports to an even higher ranking official...
If a gang member is told to do something, he just does it, no formalities.
Crips call each other "Crip" or "Cuz". Bloods call each other "Blood". Mexicans call each other "essa" (essay) don't know how to spell it... now they're saying something like "waay".
They have different "battle crys" or signals that something is going down... Bloods will say "Soooo Wooo"... that means, ATTENTION!! Or COME ON! There are hand signals as well.
There's no one easy answer to your question unless you know what gang specifically you want to know about.
Try a show called "Gangland" on History Channel, you should be able to watch episodes online or rent the episodes on DVD. Each episode features a different gang and has a lot of factual information on their structure, their roots, what they do, their signs, their tattoos, etc. There are also lots of books on the subject, although watch the date of the books printing as you probably want up to date info.
Hope that helps. If you have a specific gang you want to know about, maybe I can help you more. http://www.history.com/minisites/gangland