How do you save as .fon and .otf?

I guess the description is a bit ambiguous.

This professional font editor allows you to create and edit TrueType and OpenType fonts.

You can edit and create Truetype fonts, but you can only edit OpenType fonts. To add OpenType features to a font requires third party software such as VOLT or OpenType Compiler.
You cannot save bitmapped FON files from FontCreator.