Events are the missions and actions are what you do in missions. That is an example.

obj_char_create_1 Executes the command inside when the object is created in the room.

If theres action_message("Hello Y'all"); script in Create event and if you place this object to the main room (first room on the Rooms list), you will get a message box saying Hello Y'all when you start your game.

Other events:

  • Step: the game loop (every frame these actions are executed)
  • Alarm>Alarm x: triggered when Alarm x is going off
  • Draw: customize the drawing that GameMaker does