The email instructions say:
2. Download VOX Player for MAC
3. Click on the Loop source inside VOX player
4. Upload your music by clicking on the ‘Upload’ button or simply drag & drop.
I've clicked on everything that I can think of in the player and have been unable to find the "Upload" button. Player 2.4.1 build 2410.41 MacPro 10.9.5.
I looked for a user manual. One answered question says that the manual is available via the Vox help menu. However all options there just send me to the website, and I haven't been able to find anything there.