Understanding when to use interfaces, abstract classes, and internal classes.

I've been learning Java and I understand what interfaces, abstract classes, and internal classes can do. I just wonder when to use each of them.<br><br>For example, using interfaces, I can create a base class for my other classes with some methods I can inherit, but I can also do that with abstract classes. When do we use inheritence instead of interfaces in our classes? And when do we create internal classes inside another class? What's the prurpose of doing that?<br><br>Do some people need to use multiple programming languages to code the same project? When do we use coding languages besides Java? For example, what does Python specialize in? Does some code need to be written in other language?<br><br>Where would you use interfaces over abstract classes, how would you decide when to use which? Excuse my ignorance I'm only 2 weeks going in the learning process of programming.