The variable - it is probably a boolean - is by default eitehr just true or false (I guess you want it initially to be “false”) which you can set when you create it in the game mode. think of that as your central memory in the game - that big synthetic brain that secretly hovers high over your game and always watches you - everyone can access or edit it from everywhere that way.
Yeah when you got it in your game mode you can read or set the variable from pretty much anywhere - you just “cast” to your “GetClue” or “SetClue” function in the game mode (it is possible, but try to refrain from directly changing variables from the cast, make a function in game mode to get or set them). Think of the game mode as a cheap way of storing global variables you can access from everywhere.