CLAP plugins can be loaded in an effect slot using the slot's down arrow. The CLAP plugins appear in the effect selector's Plugins section.
CLAP plugins are bundles, the name ends with .clap. They're located in the user or system Library/Audio/Plug-ins/CLAP folder.
You can create the CLAP folder yourself if it's not present.
For plugin developers
The CLAP plugin API is available at https://cleveraudio.org
Almost all extensions are supported, except for the draft ones. The draft context-menu, param-indication, plugin-invalidation, preset-discovery, remote-controls and track-info extensions are supported.