Need help to get a job

Today I had a job interview.
And it went fairly well, I got nervous in the beginning of the interview and he told me I don’t need to worry.

Reason why is because he knew I am only a junior and he only wanted to know what I know.
So we continue the interview and basically I can get the benefit of the doubt IF I pull hard and work my ass off.

One thing he wanted me to learn now is OOP.
So can you guys help me learning the correct way using OOP in a big project ?