How to use symbols

[b-gauthier]

Hello,
I'm wondering how to use the symbols we find on https://squidfunk.github.io/mkdocs-material/conventions/.
They are used everywhere in the Material for MkDocs documentation but I'm not able to find a way to use them in my own doc.
Thanks!

[alexvoss]

This is becoming a frequently asked question, answered here, for example: #6724 and here: #6544 (comment)