On Steam it is genuinely one click. Open the Workshop page, hit Subscribe, and the next time you open the Paradox launcher the mod is in your list waiting to be added to a playset. Nothing to unzip and nothing to configure.
Off Steam — GOG, Epic, Game Pass — it is about five minutes of copying a folder and writing one small text file by hand. Both of my mods have a page that walks the whole thing: The Long Night and Supernatural.
The part that trips up almost everyone is not installing a mod. It is the load order. CK3 resolves conflicts by letting the mod lower in your playset overwrite the one above it, which means a mod that appears to do nothing is usually being overwritten rather than being broken, and sorting two incompatible mods rather than disabling one of them leaves you running a mixture of both.
I wrote up the whole thing — load order, what a game patch does to a mod, finding the one bad mod out of forty, and how to read the error log — on a separate page: when CK3 mods break. It applies to any mod, not just mine.