Regarding HTTP Adapter in PI 7.3.1

Hi friends,

     I am working in SAP PI 7.3.1. I am doing a HTTP to FILE scenario. I am encountering a problem while configuring the sender HTTP adapter.

1) What must be given in MAIN Payload parameter name in sender HTTP_AAE adapter?

2) Also when do we go for POST or GET methods.

3)Apart from this, in the HTTP client request, what must be given for the following parameters( Actually i am sending only one file )

     a)Main payload name

      b)Email

      c)client

I have attached an image regarding the same.

Help me to solve this issue.