I did something like this in C++ by following a tutorial once.

You could create an enum that holds your states, and then create a case or if else statement that has conditions for each of the state. Meaning for the start game state you'll have your main game loop, something like that.

You'll also need a loop that goes through an checks for whether a specific parameter is met, meaning if you are trying to meet a score you'll need a loop that checks for that score to switch the game state.