The YoYo Account is a one-stop login for all YoYo Games services, including GameMaker: Studio 1.4 and GameMaker licensing (through Steam or the Desktop version) as well as the GameMaker Marketplace.
Please note that versions of GameMaker previous to GameMaker: Studio 1.4 are not able to be used with the YoYo Account.
You can find out more about the YYA (YoYo Account) here: Creating A YoYo Account
Tip: If you believe you have an account but are unsure then please try creating an account with your email address, it will then notify you if the email address is in use.