The skill provides voice control of a single Logitech Media Server and any Squeezebox devices attached. It allows listing and selection of individual playback devices and the loading, playback and control of tracks, favorites and playlists as well as control of player settings such as volume and power. See Getting Started for more details
As part of the philosophy behind the project, there will always be a free version. On the free plan, users have access to almost all the main functionality, (lifetime members get some extra toys), but the skill is limited to executing around 40 commands per calendar month. Enough to get started, try things out and continue if light use is all that's required.
Upgrading to the unlimited version removes this restriction and helps pay for the maintenance, hosting and ongoing development of the skill.