I'm trying to learn the Morse Potential at the moment, but I'm struggling with a couple of concepts in this area. Could anyone please explain to me the concept of a potential energy well? I'm getting confused with all of the variables in the Morse potential equation, such as D_{0} and D_{E}, as well as r and r_{e}

Thanks in advance.

Edit: Why is it, for example, that two atoms in a diatomic have a really high potential energy when they're really far apart?