Those are the credentials by which someone could access your Asterisk Manager Interface (AMI) or your MySQL database. The default settings for FreePBX disallow public access to the AMI but normally people wouldn’t post credentials here anyway.
“How can I use it ??” - you can’t. Those credentials are for FreePBX to use. If you want to access AMI you can set up a new set of credentials in the Settings -> Asterisk Manager Users menu, and if you want to directly access the database (not recommended) just do it as root or set up a new user.