Understanding minimax with alpha beta pruning

Sorry for the image, it's straight from my notes.

I've been reading over minimax trees and alpha data pruning for the last day and a bit in preparation for my project. Which is an implementation for Othello in c.

I have read a ton of resources about it, and I know it gets asked a lot. Before I start my evaluation functions I would like to understand this fully.

In the attached image, I cannot figure out what the function Min_Node(pos) and Max_Node(pos) would do exactly, any input would be greatly appreciated.

If anyone has any tips or things I should look out for when implementing this and my evaluation function for Othello, I'm willing to take any help I can find.

I managed to figure out what max and min node was, in this case, Max_Node(pos) checks to see if this is the player, and it returns true because this should be maximized and Min_Node(pos) checks if its the opponent, if true, then it should be minimized.