Main Project Step 2 - Plan your Game Engine
For this week: Take the game idea you described in the previous step and begin breaking it down into objects and methods.
Of course the constructors and methods you're writing now will not be carved in stone. I guarantee they will evolve as you start writing your actual game code. The point of the exercise is just to get you to start thinking ahead.
For instance: Say I was writing a turn-based strategy game where a player has some number of Units; each unit has a set of Orders that it's capable of. The player clicks on each Unit (in any order) and chooses an "Order" for each one from a menu. Once the player is happy with the orders for all their units, then they click a "Done" button. Then all of their Units will execute their Orders, the player's turn ends, and it becomes the opponent's turn.
The skeleton of some of my key constructors and prototypes might look something like this (very, very rough draft)