so I have installed the plugin - but see no way of actually putting an icon next to a category. Under manage categories, there are images - but not related to FA or svg. Im using the default light theme on self hosted install. Ive read this which is exactly what I want - Category Icons
Surely I should be able to edit a category and pick an icon or put in the fa-mug or whatver code somewhere?? Hoping Im missing something really obvious
Hi, welcome 
If I understand, you have installed the Category Icons component, right?
If you want to configure the Category Icons component, go to Admin → Customize → Components and select it. The settings are there.
that is correct. I can get the question icon next to the General category - but nothing else. They are not in FA format - so how do I see a list of icons that I can select (along with their code)?
Once added in the icons section - what needs to go in SVG bit??
If I want to add this FA icon for example - how would you do this??
It is very strange that you dont add an icon in the relevant category section (where you assign images!), but in a them plugin. But Im hoping this is just a learning curve as a new user 
The documentation assumes that you know things like that
What you are looking for is Font Awesome 5 icons, as the description says: Find the Perfect Icon for Your Project in Font Awesome 5 | Font Awesome
Any icon you use in the category icon list setting, you add to svg_icons.
For example:
What you see:
Remember to provide the category slug, not the full name!
You can see the slug in the URL or the category setting.
I completely understand! This functionality is not part of the core, and a way to customize Discourse is by installing Theme components. This guide might help you to understand better:
thank you - this is very helpful. I will give that a go and see how it pans out! I was under the assumption that the SVG list was FA5 and the icon list was built in as it does not mention and isnt in the FA format. Another learning point!
thanks - this has worked a treat now I know how it applies. I will no doubt have many other questions in the near future, dont go far 
