Plumbing Shower to a Bathtub in my basement?

I current have a standing shower in my basement and I want to put in a bathtub. I know that i can do the hot/ cold water going into the tub, but Im worried about the draining. Basically, I need to know what is necessary to have a tub in my basement. I really don't know if it was roughed in for a tub or shower.