Thread adapter for Nikon D40?

I bought a Manfrotto 190XDB Tripod for my Nikon D40. I opened it excitedly, only to find out my camera wouldn't fit on the screw part. My friend informed me I need an adapter. Unfortunately, I don't know what adapter to get- I don't even know what size I need. Does any one know what size I need to get my D40 to fit on the tripod securely, or better yet, the actual adapter (I'm on a low budget)?

I'm working on it ok <.< pawn

You do NOT need a thread adapter.

What has happened is you forgot to buy a tripod head. You will need some kind of 3-way head. The 1/4-20 mounting screw is unversal and will fit your D40 perfectly

I found a used Manfrotto 3-way head for a friend (replacing their ball head) for under $35 at a camera store about six months ago