# OIS Fixed Rate - how to calculate on trade booking?

I am trying to understand how the Fix rate on a OIS trade is calculated at trade initiation. I understand this process for a Fixed V LIBOR trade non collateralized ( discount and projection curve are the same ) but get somewhat confused here Particularly in reference to the curve that is used, what are the instruments used to build from, how is it built, is the same curve then used for discounting the cashflows as projection.

Thanks