MySQL processes are created via the MySQL panel of our member site. For a description of our MySQL pricing, see this page.
Within a MySQL process, you will have full administrative control and you may create as many databases as you wish. One process is more than adequate for most uses, including supporting web sites, each with multiple unrelated applications, such as forum software and blogging tools, but you may add more if you wish.
We do reserve the right to limit excessive MySQL usage that disrupts other members. MySQL is very efficient, so this is rarely an issue, although it can come up if a process is using large tables that are not properly indexed.
(For information about the difference between a MySQL process and MySQL database, please see this related FAQ entry.)