The best way to learn OOP is just to write object-oriented programs. Re-visit software you have already re-written and see how you could re-factor it to use OOP concepts and practices. As well as this think of some real life examples to practice things like objects and inheritance. For example, why not create a car class and have it inherit from a class called vehicles which contains some general vehicle methods and properties.
See if you can figure out how to do this. I know it might seem hard but one of the best ways to learn something like this is just to dive into the deep end and see what you can figure out.
If you have any more questions then don't hesitate to ask them!