The format for each line is:
ascii character code:start x:start y:width:height
Creating the file requires any image editor that lets you put the characters you want into. You want to make the letters white (to allow coloring them dynamically) and save as a png file with no background behind the letters.
You can also do extended fonts. For both the regular (ascii codes 0 to 127 allowed) and the extended (ascii codes 128 to 255 allowed), you use the SetTextFontImage and SetExtendedFontImage, respectively.
Your English is fine. Certainly far better than any attempt of mine at Russian.
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master