Here are some things you can do to start making games in GameMaker:
- Read the manual
- Look for beginner tutorials on YouTube
- Play around with the program
- Buy a beginner course on Udemy
Do note that your first few games will definitely not be great, especially if it is your first time using any game engine. So just focus on making something, and learning how the engine works (and how coding works, if you’re new to it).