Finally, I got an invite of Google Music 3 days after request.
For every user, Google Music only allows you to invite 4 other people to join it, and my invites were all sent out, but you can still request one from it by following the above link. This post will show you how Google Music work indeed.
After registration, you can choose and import over 280 songs of about 250 albums from nearly 200 artists and in 16 genres.
For the imported songs, you can listen, mix, thumb up or down them, you can edit their info, delete them, add them to your playlists, or shop them by Google Shopping.
That’s nearly all what you can do on the Google Music Beta site, but another one interesting feature is that you can upload your own music from your computer to your account’s library with Music Manager, which you need to download and install.
After installation and signing in to your account, you can upload your songs from iTunes, music folder or any other folders to your Google Music’s library. By the way, if you are in China, you maybe need to use VPN services to connect the Music Manager client.
Comparing to Google China Music and Google India Music, Google Music here means Google US Music only (though Google doesn’t name it this way), and it is not available for you to view the lyrics of those songs that are playing, nor to download the songs there.