I need help caring for my cactus?

I just bought a cactus. It is very small. And has a green stalk and a red bit where the spikes go. I want to know how to care for it. How much water it's needs and how often. Also how much sunlight and any other useful information that i will need to care for it. It is in a small pot with holes in the bottom by the way. I'm not very good with plants so don't go really technical. Thanks