Up against competitors such as Spotify, Microsoft may have to play catch-up in terms of functionality, as users are already frustratingly reporting the lack of a preview function. A useful feature is the ability of the client to read music stored on local SD cards, a handy feature if your tablet is running low on memory. The rest of the functionality is mostly what you'd expect to come by default – a search function, organization and playback of playlists, etc.
Upon your initial sign-in, your entire library should quickly follow through and synchronize, if you're an Xbox Music Pass holder and already sport one. If not, a free 30 day trial is available for you to take a look. There's currently no ad-supported web version of the app, therefore a $9.99 subscription is what you'll need to cough up for the service.