I just bought a little pet snake, what should i put in its cage and what do i feed it

a water bowl

some sort of flooring (either astroturph or aspen mulch-cedar can kill snakes)

a place to hide-it can be as simple as a butterdish placed upside down or a flowerpot on it's side.

It will likely need a heat source unless you are in a hot climate-and the pet store can tell you based on the size tank you have.

It's best not to try to feed it for several days-you are better off just buying the snake and leaving it quietly with water for a day or two. But use that day or two to read everything that you can about it.

The thing is, you did buy the snake before you researched it, but you are asking now, and that is a very good thing. Good luck to you and your new friend.