Like Request, HTTP Response has three parts:

• Status Line
• Headers
• Message Body

The Status Line indicates what happened. It is made up of three parts...

• HTTP Version
• Status Code
• Reason Phrase - a description of the Status Code

There are a bunch of Status Codes that all fall into basically 4 groups

• 2xx (200-299) indicates a success. That means it worked. The different codes indicate specifics (accepted/created/partial content/...) but any 200 code is good.
• 3xx (300-399) indicates redirection. Means the resource requested has been moved, deleted or not modified. e.g. 304 Notmodified is is returned if the browser was refreshed and the page didn't change.
• 4xx (400-499) means the client has a problem. Bad Request, Can't do it, unathorized, etc.
• 5xx (500-599) indicates the server had a problem servicing the request.

Here is a complete list of HTTP Response Header Fields. Also WIKIPedia has a good write up on HTTP Header Fields for both request and response.

There has to be a blank line, that is 2 line feed/carrage return combos between the header and the payload in both the request and response messages.

The message body or the payload is the response from the server. The meat and potatoes. The Jack Pot. It's what the client asked for.