After you have downloaded the Game Maker software, you will need to set up a password on your Sandbox account to be able to access the Game Maker. Unlike on The Sandbox's website, you will not be able to use your cryptocurrency wallet as a login method for the Game Maker.
If you have not done so already, you can download the Game Maker from here: https://www.sandbox.game/en/create/game-maker/. Then follow the steps below to get started.
Log into your Sandbox.Game account. Or register for one if you do not already have an account.
Once you are logged into your Sandbox account, go to your profile: https://www.sandbox.game/en/me/profile/.
Once on your Sandbox profile, click the three dots that appear above your profile's cover image. Then click Edit.
Now give yourself a password by filling in the fields in the settings prompt which appeared.
Now open the Game Maker software. When prompted, log in with the email and password that you gave yourself on your Sandbox profile.
Once you have logged into the Game Maker you can now begin creating and editing your experiences and publish them.
See this page for links to helpful Game Maker tutorials and guides: