What it does
CMS is the foundation module -- it's enabled by default and can't be turned off, since every other module's public pages render through its theme and layout system. It covers pages, navigation menus, media, and schema-backed content blocks (hero, feature grid, stat grid, timeline, image).
Using it day to day
Pages are built from an ordered list of blocks, each with its own small schema -- you don't write raw HTML for a standard page. Pages support draft/published status, scheduled publish dates, SEO metadata, and full revision history. Content can be exported and re-imported as portable JSON bundles.
Install and update
CMS is always on -- there's no enable step. Updates arrive the same way as the rest of the platform, as part of a whole-platform release.