Docs: tween

Tweens are animations of variables. For example, You can create a tween to animate the "x" position of the object obj_box, during 2.5 seconds, from the actual position to the position x = 200.

tween_to( obj_box, 2.5, ["x", 200]);

This will create an animation for the all the obj_box instances during 2.5 seconds. And then, it will be automatically cleaned up for you.

You can also create a tween, and store it's reference in a variable. Then, you can use it to play, pause, seek, and reverse a tween.

mytween_from( obj_logo, 2.5, ["scale", 0]);