How to care for an Orchid?

I just bought an orchid from Kmart. Its in its original packaging which is a small plastic square pot. I unwrapped the cellophane stuff around it and its potted in what the tag calls volcanic cinders. Anyway, the roots seem to be popping up out of the pot. I dont know how to grow these and I love it and wanna keep it alive. Do I need to repot it or just put the roots back down into the plant? Help and advice on how to care for this is much appreciated!