If you wish to have a Microsoft-Account-linked Win10 User Account then a Microsoft Account must exist to which to link it. The userid is generally the e-mail address you're using and if the corresponding Microsoft Account does not exist you should be prompted to create one. If it does exist then the linked Win10 user account will be created and the password should be the same as the Microsoft Account to which it links.
You also have the option of setting up a local account, too.
If you activate the option for adding a family member, this is the first dialog you encounter:
whereas if you activate the option for someone else this is the first dialog you encounter:
Brian AKA Bri the Tech Guy (my website address is in my profile) Windows 10 Home, 64-bit, Version 1709, Build 16299
Here is a test to find out whether your mission in life is complete. If you’re alive, it isn’t.
~ Lauren Bacall