How do I connect to a database?
The most common database used with a Xoops installation is MySQL, an excellent open source database.
To connect you Xoops installation to a database you need three items:
1. A database name.
2. A database username
3. A database password.
All of this information is stored in mainfile.php so Xoops can automatically connect to the database as needed.
This Q&A was found on XOOPS Web Application System : https://xoops.org/modules/smartfaq/faq.php?faqid=99