MySQL
MySQL is the best database management system for managing linear databases. What?
You'll learn MySQL as you go, it is useful for placing database entries and making them easy to use for everyone. Tables of users, chatrooms, and more all can be stored with MySQL, and any use of a non-linear database (one line has more columns than another, or other things which make the table look less like one line on top of another, and more like it is non-linear, in that regard of table columns. The rows are - and the columns are |, by the way).
Have fun!