In a broab sense, an IP address is like a postal address...
When you send a postcard, you can't just say "Send this to evil_d00d", you have to tell the post office how to find you. Same with the internet - when you (for example) want to look at unix.com, behind the scenes, your web browser will ask a domain name server "what is the address of Unix.com?". The name servers replies "64.23.37.23".
But which is easier for you to remember, "unix.com", or "64.23.37.23"?
Search google for more specific (and technically accurate) information. For example, here is the results of a search on "TCP/IP tutorial":
http://www.google.com/search?hl=en&q=TCP%2FIP+tutorial