My mom just gave a used rice cooker for christmas and it didn't come with any kind of instructions. Where can I find them?

You cooker should have a lever , down to cook rice , it will "pop" up when the rice is done, allow to sit 4-5 min to allow the rice to finish steaming.

2 cup med grain rice & 3 cups water yeilds about 6 cups cooked rice

You can download the manual for the RC400 at this URL

http://useandcaremanuals.com/pdf/RC400-RC550421.pdf

As for the rice measure (if you don’t have one). My rice measure (and I think most) is 6 ounces = 3/4 of a standard cup.