It's weird, isn't it? It seems like you should be able to use More Ascent and More Descent multiple times to get some height (assuming it starts at zero ascent and descent), and then use Insert Character to add the first character, and then, once you've got that character in view (by clicking on the right side until its ASCII code is at the bottom), use Insert Column a few times to give it some width and then start adding pixels. But it just keeps incrementing the character code and nothing else. Or, get to a character and try and insert that character, and it just crashes.
It makes me think that there is a file you're supposed to start from, like an empty bitmap or something, that you prepare first in some way. And maybe that's why it beeps when the windows appear after you provide a font name when you launch the app.
Wait: I just discovered something. When it asks for the name of a font when you launch the app, it wants you to provide the name of an existing font document and the size of the font in that document. If you do this, it opens the font document dutifully with no beeps.
Maybe it's not possible to make a font from scratch, that you are meant to always start from an existing font. That raises a chicken and egg question, but the developers of the Mac must have had a way to make a font prior to the existence of Font Editor. So maybe they leveraged these earlier fonts to make the later ones. In other words, it could only make a new font from an existing one. The fact that there is no New Font... command is evidence for this.