How to simulate POST request by Chrome apps Postman

I'm testing on Windows, trying to simulate POST requests (with different form variables) for load testing. I have tried all kinds of load testing software but failed to get it working.

For GET requests, I know I can just put parameters behind the url

http://www.example.com?id=yyy&t=zzz

But how do I simulate a POST request?

I have a chrome REST Client but I do not know what to put in the headers and data.

Here's what I've tried so far: