It is always best to use the Accounts & Privileges that already exists in FMP to manage login.
Define a startup script that then looks at the account name and steers to where you want them to go:
If (Get(AccountName) = "Mary" )
GoToLayout (Mary's Layout)
If the tutorial said to define fields with usernames and passwords in a table....well....find a better tutorial.
Each user should have their own account & password. You can use Get(AccountName) to direct behavior after that.