Very close..need help implementing Minimax AI

So after reading couple blogs about Minimax, such as, conceptually I understand but with my current code, I’m having hard time executing with it.
As of now, I have a very simple Computer AI that just randomly picks any available moves in the current state.
Can anyone give me a hint/tip on where to start? I would assume creating something like a new State object but not sure…

I liked this video An Intro to Video Game AI for Beginners and Young Programmers