Networked Multiplayer, best starting point.
Kiddddinnnnnggggg
Where you should start depends on where you'd like to go. Similarly, let's say you want to learn to run.
"Hi, I'd like to someday run a marathon" -- "Start slow with distance, 1-2 miles for a week, and then add a mile per week up to 12 or 13 miles"
"Hi, I'd like to someday run a sprint relay" -- "Start with core and upper body strength building/lifting, and quickness drills for your legs"
Both are running! How to get going depends a lot on the kind of running....
If you want to get into making games from the point of view of designing systems, logic, that kinda stuff... Making that simple platformer or Breakout game is a great way to start. You get to try out movement code and collision code and all of that jazz, and see how your expectations and GameMaker's implementations intersect. You work out all the bugs with something that has very few parts to it, then build up.
You can easily add stats to a platformer once you know how the mechanics of the platformer work. Too often, people start with a platform tutorial, already made, and then want to know "how do I double-jump? wall jump? add armor to my character?" And they haven't worked out how the existing game functions yet, so it *seems* challenging to expand the mechanics.
If you're interested more in designing experiences, visuals, and stories, then you can look towards point and click adventures or visual novels. GameMaker is set up in a way that makes it verrrry easy to drop some images into your game, and to make them appear and disappear. Actually, I showed a friend how to make a basic visual point and click adventure in less than 10 minutes yesterday with a single object and a couple of rooms. If you want to focus on story and atmosphere and not get deep into wrangling with mechanics, that sorta game might be a good intro to GameMaker...