If the software is pre-installed, you should be able to just go ahead and launch FileMaker. There is nothing to activate. You only need a license key if you need to install FileMaker.
If you can indeed open filemaker, you can go to the Help menu and select About FileMaker | Info to see the license key. I'd write that number down and put it in a secure place, just in case I ever have to re-install the software.
If the software was not pre-installed, I'd contact FileMaker customer support by phone for their assistance.
There is a FileMaker Pro 11 folder in Applications, containing the application. When I open it, I get a window that says I need to enter my name, user organization, and the license key. So I never get to open the program itself. I suspect whoever at Apple was supposed to install it just copied the files to the disc and never completed the installation.
FileMaker Support is only open from 9 to 5 and so I've missed another day to call them. Darn.