How can I make a font for graphical LCD?
If you are asking how to make a font, there are a number of utilities out there. Here are a few:


DotFactory is simple, free, and does a good job converting existing font files to C code.
BitFontCreator is a low cost tool with a graphical font editor, you can convert and edit existing fonts or draw your own fonts and symbols. Very versatile. I like it and I've used it a lot. 
NXP offers a free version of the high end Segger GUI tools for use with their ARM processors. It includes a font editor. There is a download link on this page.


If you are asking how to use a font library, that is hard to answer without more details. In general terms, the font tools produces a big array that contains the pixel position for all the characters in the font. It also makes a jump table that tells you where each individual character starts within the big array and how wide it is. 
When you know the height of the font, it is fairly straightforward (depending on your experience) to pick out the data for individual characters and draw them on the display. 

If you are new to this it is best to start out with working example code and spend some time understanding how it works.

EDIT:
The microbuilder codebase has example code to get you started.