Nabix How would i go about adding links to my header? (i.e., just like the flarum site here)
https://github.com/FriendsOfFlarum/links
Where are the main CSS files stored?
We use less https://github.com/flarum/core/tree/master/less (note that this is only core, each extension might have it's own less.
Is there documentation on theming and how to start?
Unfortunately our documentation for theming is doesn't exist at the moment. Most people end up copy and pasting their changes into the CSS box in the admin appearance section. However you could also follow the extension settings and import your own LESS that way.
My last question is, What is the best way I can support Flarum? I'm not an experienced coder; I know just enough html, css, and php to get my into trouble. Currently I'm self teaching code so I can begin to work on projects like this.
We have a list of "Good first issues" on GitHub here. I do recommend leaving a comment on any issue you plan to work on so that we can guide you as needed (joining our discord and asking there is also fine). We also accept donations via Github sponsors and Open Collective which helps more than many people relize. If your looking for some sweet Merch to support the project we also have that 🙂