While font awesome is really awesome
If you need another source for icons you can visit the noun project
Of course it takes a bit more work to use but there are over 2 millions (according to them) of icons in there
Beyond the famous font awesome icons which provides 2 main versions of icons 4 and 5 - including paid and customizable ones, and many free and popular too - , you can use build-in CSS ENTITIES with this syntax:
content: ' \numberCode';
This numberCode is alphanumerical or numerical-only 4-digits.
E.g '\27B1' (fat shadow arrow icon)
Reference with many icons, including letters:
There are also Google and Bootstrap Icons as alternative to Font awesome library. I recommend you to take a tour and get to know them all and pick up one and stick it with until you feel familiar to work with.
Here a nice introductory tutorial on icons by w3school:
You can try this nice reference icon picker of this same site:
You can filter icons by different sources and have an example embedded for every icon. I use it when I wanna find the best and suitable icon possible
Exactly like that
As long as you have the fontawesome script it will work
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.css" integrity="sha256-NuCn4IvuZXdBaFKJOAcsU2Q3ZpwbdFisd5dux4jkQ5w=" crossorigin="anonymous" />
links for various version can be found here