You can generate documentation by running cargo doc and browsing the generated web pages in target/doc. There are also examples in the examples directory of libcosmic, as well as a design demo example which is a WIP.
libcosmic is an alternative toolkit for building desktop applications and layer shell applets. It wouldn’t make much sense to build a toolkit only for ourselves. It’s the best way to develop layer shell applets for COSMIC, and other Wayland compositors that support the layer shell protocol.