Kazee
no question is silly if you don't know the answer.
I agree with Maz - as far as I know, you need to go to the Post Office and buy a Special Delivery envelope (£4.95) to send your application, passport and photos in.
You have an option to either enclose another RM Special Delivery envelope for the return or pay extra for a courier service.
Have you paid extra for the return courier service?
If so, you only need the one RM SDE to send to Hayes.
Don't forget to make a note of the reference number of the SDE so you can track (via the RM website) when it's delivered to VFS.
If you're having return by RM SDE, make a note of that number too.
How much have you paid?
Visas cost £30.00 plus £9.05 for the VFS Service charge, so you should be able to work out what you've actually paid for.
IMPORTANT:
You can only send 2 passports in one RM SDE.