Hi and welcome, tullsman 
There is no necessary developer knowledge to use Discourse. There is to develop customizations.
As @Lhc_fl said, Discourse is open source.
But also, most of the customizations (Customization > Theme, Customization > Theme component, Customization > Plugin), including the official ones, are also open source. People usually create customizations for their own needs, or find someone to develop it for them (via Marketplace, for example).
Many customizations are available for free in Discourse, and any admin who self-hosts their forum can use them.
If you are hosted by Discourse, using one of their plans, there are limitations that are described here: Discourse pricing | Discourse - Civilized Discussion