GET should be used when you are querying a server while POST is used to post data to a server. POST data is sent after the HTTP headers and looks like this:
item1=data1&item2=data2&item3=data3
So a full HTTP header would look like this:
HTTP /1.1 POST
Content-Type=application/x-www-form-urlencoded
Content-Length=46 (number of characters)
POSTDATA=item1=data1&item2=data2&item3=data3
The actual RFC spec is
here.
And after all that, I think you said you already post data so you are wondering how to handle the data once it gets to the server? If so, you need a programming language server side to handle that and you would need to determine which language you will use and ask on that board. What you are looking for is CGI programming.