The Step Event in GameMaker: Studio
GameMaker: Studio tells time by steps, which is defined by the Room Speed, which sets how many steps are performed each second. Step Events in your game are great for when you want something to continuously happen, or you want something continuously checked for each step of the game.
An example of using a Step Event is to determine if certain Instances have left the Room, and if so, to reappear at the top of the Room. As GameMaker needs to continuously check to see if the Instance left the Room, a Step Event comes in very handy to use.
When you click Step from the Event menu, a submenu appears giving you three options, as shown in the figure below:
Step: This will probably work best for you 90 percent of the time.
Begin Step: This option is useful when you absolutely need the Step Event to be the first Event checked, no matter what, every time.
GameMaker updates all built-in variables between the Step and End Step. So, if you want something to happen after the variables have been updated, then choose End Step. If you want something to happen before the variables are updated, then choose Begin Step.
End Step: This option is just like Begin Step, except it’s for when you absolutely need this Step Event to be checked last, every single time.Your Step Event options.