Are the purchase of my self published books an expense?

They are an expense, but in the Cost of Goods Sold (COGS) section.

for example:

Beginning inventory   $0

Purchases  $600  (say I bought 100 books @ $6 each). 

Ending inventory ( on 12/31/2016)  $60   (say I have 10 books left)

COGS   $540   ($600 less the $60 left).  

TurboTax will compute the COGS when you enter the beginning inventory, the purchases and the ending inventory.