Font Awesome - the basics
Font Awesome gives you scalable vector icons that can instantly be customised -- size, colour, drop shadow, and anything that can be done with the power of CSS.
We use Font Awesome for the graphics in each section heading in these courses (with a simple layering effect e.g. colour box, with smaller icon inside).
More info on Font Awesome 4 can be found here: https://fontawesome.com/v4.7.0/
Note that some Moodle Themes use Font Awesome 4, but some may support Font Awesome 5: https://fontawesome.com
How does it work?
You can enter a small string of text which inserts an icon into Moodle. There are thousands of icons to choose from. See the Font Awesome cheatsheet for the full list of icons you can use.