How can I create custom varibles and use my own php in mybb? I basiclly wanna create another box on the profile page. Thanks in advance.
Could you describe what you mean by another box? You mean like the "blubox's Contact Details" and "Additional Info About blubox"?
What would you like the box to contain?
i want it to contain information i have stored in another database
You will have to write a plugin (or code modification) to populate variables that you can use in whichever profile template you want, then.