Hi Laurence! When you first set up your forum, you should see a special default topic with the title “READ ME FIRST: Admin Quick Start Guide” (in the private “Staff” category). This contains an overview of most of the basic info for configuring your site as an admin — things like testing email, setting up categories, and sending invites.
This is also quite good as a basic guide for getting up to speed on a lot of the terminology and features, both for you and as something to point users to as needed: Discourse New User Guide
These blog posts are useful as well:
For further specific questions that arise as you get everything set up, best place to get help is right here! First thing I do is usually try some searches here on meta.discourse.org. Then if you’re unable to find existing discussions / answers, go ahead and make a new topic.