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.
