Classes: A type of something. You can create new Objects of a certain class. Example:
Animal animal = new Animal();
Entry point:
Where your program starts. The entry point in Java is:
public static void main(String[] args) {}
String:
A length of text. Example:
"Hello World!"
Variable:
Like a box which stores a value. Example:
int hello = 0;
You can also do this:
int hello;
But then to use it, you need to give it a value:
hello = 0;
Variables can be objects, too. E.g.:
Dog d = new Dog();