Answer 1

Unified Modeling Language.
In short if you want to explain your class structure using a diagram, you do it using UML.

Squares are used, similarly to database structure.
But instead of columns you enter the fields (variables and methods).

You use the "+" sign for public fields and "-" for private ones.

And using different types of lines, one would understand that there is an inheritance, implementation, aggregation, composition etc.

I personally don't like UML. It does not help you in solving problems. But it is required in schools and interviews