Font conversion

Do you mean this font converter? http://ebfc.mattbrailsford.com/

You supply a single image with all the characters in - maybe like: https://opengameart.org/content/ascii-bitmap-font-oldschool

So then:

• First character is the number of the first character in the font. So in the example above the first line is !"... (first character being a space). You look it up on http://www.asciitable.com/ and find the character code for space is 32, so put that in
  
• Width and height are the size of each character in Pixels. However in the above link it says '5x7', but the image itself is 128x64 pixels, with 18x7 characters. You divide that down and the actual character size in the file (because they're padded out) is 7x9, so that's what you'd have to use.
  
  

However I'd strongly recommend that you use http://www.espruino.com/Font+Converter if at all possible - since does all that for you and can handle antialised fonts as well