fontmaker.exe is used to generate .lmf font files that the engine can read. Typically, the license to a font states that it can be freely used but can't be distributed. This program allows you to take a .ttf font file and render it at a specified size, and then distribute the rendered file, which is within the terms of the license agreement.
Fontmaker takes a single argument, the path to a script file. This script should contain all the fonts that are used by your project. This lets you compile all your fonts with one command, and records the fonts and sizes that you use in case you forget in the future.
The script file should be formatted like this:
#this is the folder where to fonts will go