This is a Minecraft shader pack which uses fonts to render the game scene. You need optifine to enable this shader.
Try it for fun, be careful of your eyes, don't vomit if there's no toilets near you.
Goto shaders/textures folder, add your font file into your downloaded shader folder.
Your font file format should be PNG or JPG image file, every glyphs should be arranged like a matrix (like the existing font image).
After added your font file, edit shaders/shaders.properties, change the value of texture.composite.gaux1 equals to your font file path and name.
Then, if your font file have different size or glyph count, you need to edit the code.
Edit both shaders/composite1.fsh and shaders/final.fsh, change const ivec2 CharSize = ivec2(8, 16); to your font file glyph size, edit const ivec2 CharArrange = ivec2(16, 16); to your font file's rows and columns. Make sure both of the file were changed. That's all.
https://www.shadertoy.com/view/tlfXzX
Make sure you had optifine installed, then goto your Minecraft folder (which often is "C:\Users\yourname\AppData\Roaming\.minecraft"), you can see there's a folder named shaderpacks. Open this folder, create a new subfolder named "font-shader-1.0.0", then put "shaders" folder and "LICENSE" file inside this subfolder. Be sure you had read the LICENSE file and agree with it.
You need install Java first. Then goto optifine official website to download and install optifine for minecraft.
When you finished installing Java, you can just double-click optifine.jar to install optifine.