In general, variables are symbols that associate a name (the identifier) with a value. Like in:
boolean isComplete = true;
* Here, boolean is the type of the variable
* isComplete is the name of the variable
* and true is the value of the variable isComplete
However, you can not assign a value to the variable. eg:
int awesomeLevel; // Here, awesomeLevel is a variable and his type is int
int epicLevel; // Here also, epicLevel is a variable and his type is int
In object-oriented programming (OOP), a property or an attribute is just a variable that is inside a class or an object while a method is a function that is also specific to an object or to a class.
Contrary to the attributes, the methods are distinguished by the parentheses
* Here booleen is the return type of the function/method
* isComplete is the name of the method
* The value (true) between the parentheses is called an "argument"
I invite you to continue the course, you will understand better.