How can I convert a font from Font Book to .ttf? I am programming an application for IOS 5, but I need to use a different font. I found the perfect font for the job in Font Book, but it needs to be a TrueType Font file. Is there an easy way to do this?

By the way, if you can tell me how to make my own, I would appreciate it.
Font Book is an application, not a font format. Some fonts that appear in Font Book are True Type fonts. For those that are not, the question is about converting that specific format.

To find the file for a particular font, select it in Font Book, control-click it, and select "Show in Finder". You can then see what the format is on the file.