If you get the time to google "what is REST" you will find an overwhelming amount of information, in fact as of today google shows that there are about 1.16 billion results!
These are just some of my favorite resources and I'll add more in the future; there are a wide range of resources varying from conference talks to specs to tutorials and more.
What is HTTP:
You should really start by understanding what HTTP is:
- HTTP: The Protocol Every Web Developer Must Know - Part 1
- Hypertext Transfer Protocol HTTP/1.1 (RFC2616)