Need help understanding interior points, boundary points, isolated points, etc.

I am taking a Real Analysis class and we are learning about interior points, boundary points, isolated points and accumulation points.

I really am not quite grasping what all of these are and the textbook I have isn't much help. I was wondering if anyone knows of a particular website that clearly explains each of these things or gives some examples of each type.

Or, if you clearly understand them you could just type out what exactly each one is, explain how to decipher each one from another, and so on, to help me out.

Thanks for any help!