thekops. It's not really a matter of how to use that script step. In this case there's a few larger questions to think about.
1) Should you be storing your passwords in a database table? This is generally considered very insecure. Why are you doing this instead of using FileMaker's powerful built-in user accounts system? If you do need to store them, what sort of security are you using?
2) Go To Record/Request/Page is generally used to navigate to an already-found set of records. Since you are trying to find a record, you need a different action, like a find. In it's basic form, that may look something like this:
Enter Find Mode [ no pause ]
Go To Layout [ users ]
Set Field [ users::username ; "==UserYouAreSearchingFor" ]
If it's a matter of letting an admin user manage accounts and storing some other settings in a table, you may want to check out the accounts module:
This is a fully featured filemaker account manager, that does NOT store the password in the table.
What would you suggest then Bruce?