The computer that I had when I was at school in the 80s - in common with a lot of personal computers at the time - allowed you to design your own text character. You could use this in a game - e.g. to make a "space invader" - or you could use the same technique to make your own font. I made my own font that looked like my handwriting!
Characters were designed on an 8 x 8 grid, and created using eight numbers from 0-255. Each number was converted to binary and the resulting pattern of 0s and 1s was used to make a pattern of black and white dots on a single row.
You can design a character in the same way by entering numbers from 0-255 in the boxes to the left of the grid. Each number is converted to binary and used to create the pattern of dots.
Fonts on a modern computer would be made up of a lot more than 64 pixels, but the principle is the same.
If you can't see how the numbers are converted into the patterns of black and white blocks, try looking at the page on binary. If you can see the link between the number and the pattern, then think about how the web page works - maybe you could create something similar in a spreadsheet application?
There is a similar page that demonstrates how an image is stored.