How do I see what parameters and data are needed to send a POST request?

I am trying to look into what happens when I hit a next button and what info is sent to the server and sent back. I am using the chrome network debugger and I found the file that returns:

Request Method:POST
Status Code:302 Found

I don't see anything regarding that in the headers. I need to find out what is sent to with the POST requests so I can send my own through an app of my own. Please tell me how to find what I need so I can send my own POST requests.

(the file is a .aspx)