How is an HTTP request structured?

An HTTP request is plain text: a request line naming the method, path and version, then header lines, then a blank line, then an optional body.

When you load a page, the browser sends something like this in readable text:

GET /hello.html HTTP/1.1          <- request line
Host: example.org                  <- headers begin
User-Agent: Mozilla/5.0 ...
Accept: text/html,application/xhtml+xml
Accept-Language: de,en-US;q=0.9
Accept-Encoding: gzip, deflate
Connection: keep-alive
                                   <- empty line separates headers from body
[request body - optional]          <- e.g. data for a POST

The pieces:

The method in the request line declares intent:

• GET — retrieve a resource (no body needed).
• POST — send data to create something (uses the body).
• PUT — replace / update a resource.
• DELETE — remove a resource.

Gotcha: that blank line is mandatory — it is how the server knows the headers ended and the body (if any) begins.

Go deeper:

• HTTP messages (MDN) — annotated anatomy of the start-line, headers, blank line and body, for both requests and responses.