HTTP for Dummies??

I've been looking over RFC 1945 to try and learn a detail or two about
HTTP, and it occues to me that I'm not very bright. Specifically, I'm
trying to find out how the value to specify in the Content-Length line
when POSTing data to a form (I'm trying to do a POST in Java using a
Socket, not a URLConnection). The meatiest thing I've found is from
section 10.4:

	The Content-Length entity-header field indicates the size 
	of the Entity-Body, in decimal number of octets, sent to 
	the recipient or, in the case of the HEAD method, the size 
	of the Entity-Body that would have been sent had the request
	been a GET.

That just doesn't do it for me.

Is there an HTTP reference anywhere that's a little simpler?

Thanks,
Chris