How to I add a single to my album?

You should first upload your single, once the single is delivered it will be issued an ISRC code. Now you can upload your album and for that particular single add the ISRC code issued. For the rest of the songs that are new, request an ISRC code. When you use the same ISRC code, your stream counts will combine and you can see the song under singles with single artwork and you can see the song under album under album artwork.