You must insure that you have the the X11 server installed on your system.
Continue
until you get to the pane "Custom Install
on "Macintosh HD""
Continue
You may also want to install the fink package which includes many useful libraries (see the dependencies section below for more info on this)
I post a mac install package on sourceforge's file release system. There's a certain amount of pother involved in using the file release system, but you get the file eventually.
Generally your browser will decompress the package after pulling it down, and then start the install process itself.
If this doesn't happen, find the package (it's usually on the desktop) and double-click on it.
The install will request your password (to make sure you have the right to do an install on your machine, and then ask some innocuous questions, and proceed to install.
FontForge does not conform to Apple's Human Interface Guidelines. FontForge never will. Don't expect it to look like a normal Mac Application. It doesn't.
Before you can start FontForge you must start the X11 server. You do this by opening the Utilities sub-folder of the Applications folder and double-clicking on X11. This will bring up a new menu bar, and under the Applications menu you should find an entry for FontForge.