I don't mean to insult your intelligence, but without specifics I just have to explain all the basics. I recommend, if you don't have an artist handy and you need to make your own assets, getting an art software that is good for pixel art (Aseprite is what I use). You can also check check out the Community Assets repository. You can just go into your project folder once it's created and put .png files into the appropriate places in your project's "assets" folder.
I'm assuming you can run the installer and find the program. Once it's open, There are three templates you can choose from. If you don't want to repurpose their prebuilt example games then I suggest choosing the blank template. Change the project name to whatever you want and click "Create Project." The Studio points you to a "+" sign in the top left of the UI. Click that and then click the empty space in the middle, that will create your first scene.
After that it's kind of up to you. GB Studio is very user friendly and does a lot for you automagically. For more functionality than just having collision, unresponsive NPCs, and a moving player character in a white void, you'll need to use programming. GB Studio uses drag & drop blocks, no language knowledge really required. There's even a handy dandy search bar so if they have it, you can find it pretty quickly.
Checking the docs for GB Studio would be a good start if you need specific explainers for particular functions/aspects for the program, it's here: https://www.gbstudio.dev/docs/.
GB Studio Lab has some tutorials I found useful for more advanced stuff you'll need to learn actual scripting language for, it's not too bad though. I believe you can also make custom plugins in Typescript and assembly language, though don't quote me on that.
For even more you can check out projects and templates others have done that you can download directly and open in the Studio. I just completed a basic Blackjack minigame that could help you (if you can make sense of my spaghetticode) and it's on my page here on itch.io, it's free unless you feel like donating. If you need help with programming, I'm sure I can answer, but the internet is full of people much smarter than me.
Hope some of this is helpful :)