Triggers are the starting point in a chain of logic, often initiated by a players input.
If we consider that Logic is the sequence of events inclusive of the input, the message, and the outcome, then when we refer to Triggers we are talking about the specific moment - the singular event - that initiates a chain of events.
For example, flipping a light switch would be considered a trigger. Only once that action has taken place does the electricity get sent and the light turns on.
This would be the same if you think about lighting the fuse for some dynamite. Lighting the fuse is the action - the trigger - the fuse then carries the message, once that message is received the explosion is the outcome.
While this is an important step in creating a sequence of logic, it's also valuable to remember that the action is independent of the outcome. There could be other circumstances established between the action and the outcome, such as the wire being cut, or the fuse being put out, that would change how the outcome plays out.
What’s interesting here is that, if we add a layer of complexity to this relationship, the outcome could also be used as another trigger. For example, an explosion could also be what triggers another sequence of logic, such as destroying other objects, and that too could Trigger another outcome.
Keep this in mind as you continue your journey through the Game Maker. As you become more confident with how one action can lead to another, you’ll find you will be able to layer more complex connections on top of each other to achieve dynamic experiences.
The trigger is the action that leads to an outcome, and, in this case, we need to be aware of a few important sections in the Game Maker that allow us to define a Trigger, specifically understanding Tags and Messages.