Adding tracks is very simple. Make sure you are within your profile to upload music. You can either access your profile by clicking on the MDIIO icon within the top left of your screen or through the dropdown. 

You can either drag your songs from your operating system or click "Select Track(s)" to upload. 

You can go ahead and close this window while your music is being uploaded. You'll find your music on the right-hand side of the profile screen. 

You're set! Please ensure metadata is added to music to have a greater chance of getting discovered.