To send music to someone's Spotify Inbox, you need to have him in your People list first. Because you can add anyone who has a public profile to your People list, you may be a stranger to your recipient (and you might receive tracks from people you don’t know).
When you click the People link ion the left-hand sidebar, all your Facebook friends are displayed in the main pane, along with any public profiles you may have manually added. You can hover over a friend’s name and click Add to Favorites to add them to your right-hand sidebar. This makes it easier to send tracks to them and view the playlists and top tracks displayed on their profile pages.
Once you’ve added your favorite profiles to the right-hand sidebar, you can easily send them tracks, playlists or albums. Once you find the item that you want to send to a Spotify friend, click and drag it to that person’s name in the People sidebar. A dialog box pops up, which includes a text box where you can add a brief optional message. Click Send Track (or Artist, Playlist, or Album) when you finish adding your message.
Alternatively, you can click the People link to view all your Facebook friends (and other Spotify profiles you’ve manually added) in the main pane. Click a name to access her profile. Your top tracks are displayed by default. Click Send Track under a desired song to send a link to that track to your friend (they need to have Spotify to be able to play it).
Alternatively, click Search for something instead to manually search for a track, and send it that way. You can include an optional message.
Alternatively, click a Share icon anywhere within Spotify and, in the pop-up window that appears, click the Spotify tab. In the To field, start typing the name of the friend to whom you’re sending the item — a drop-down list of recipients from your People list appears; select the friend you want to send it to.
In the Message text box, add an optional note, and then click Send Track (or Artist, Playlist, or Album, depending on what you’re sending).
To send more than one item at a time, Ctrl-click (Command-click on a Mac) the items that you want, and then click and drag them to the person’s name in the People sidebar. Note that you can’t send more than 100 tracks at a time, and you can send tracks to only one recipient at a time.