How to show simple binary operator in first order logic?

Hey guys, I'm just a little confused on how I express binary operators in first order logic.

Heres the question:

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Let G be a set and " * " a binary operator on G.

Show the following statement in first order logic:

for all f,g ∈ G, (f * g) is an element of G.

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I defined set(x) to be true if and only if x is an element of G.

This is how I started the answer:

∀f ∀g ( set(f) (and) set(g) ----->

How do I express the binary operator here?

Thanks for any help!