banjobama is correct in that you cannot create/delete Collections directly within the PRS-900. You must use the Sony Reader Library which sucks or Calibre which is somewhat cumbersome. I'm not sure what the Sync function actually does, but I accidentally used it once and wound up with a mess I can best describe as scrambled eggs. That is probably because I had both a 900 and a 300 and I think it tried to sync them together even though I had different Collection names on them. Also, NEVER run Calibre and Sony Reader Library at the same time while your Sony Reader is attached to the computer. That was the biggest mess I ever had to clean up. I pretty much had to clean off everything from my 300 and start over from scratch. I had left calbre running by accident, though I only used it to convert a book. I then opened the Sony Reader Library and tried to send books to the 300. I'll never do that again!