Where do I make the inventory entries for my business

1. With your return open in TurboTax, search for Schedule C and then select the "jump to" link to go to the self-employed section. ...
2. When you get to  the expenses screen, scroll down and select Inventory/Cost of Goods Sold

Large businesses that purchase, produce, and sell merchandise to generate income usually keep inventory and use the accrual method of accounting. The inventory's value at year-end is subtracted from its value at the start of the year (plus purchases made during the year) to arrive at the cost of goods sold (COGS) for that year.

However, if your business' annual gross receipts for the last three tax years average out to $26 million or less per year, you can opt to use the cash method and expense the cost of inventory at the time it was purchased, rather than waiting until after it's been sold.

In TurboTax, you can report these costs in the inventory section as COGS or in the expenses section as supplies. Either way, you don't have to report inventory but you do need to carefully track what you paid for the products, materials, and supplies that go into your inventory.

https://ttlc.intuit.com/turbotax-support/en-us/help-article/business-tax-credits-deductions/need-report-inventory/L3JwjUlQm_US_en_US