You'll enter this under the Federal Taxes tab (or Personal, if working in TurboTax Self-Employed/Home & Business), then select Wages & Income, then Investment Income, then Stocks, Mutual Funds, Bonds, Other. Follow the prompts to enter the 1099-B information. This will require an upgrade to TurboTax Premier online, since a Schedule D will be prepared.
More info: https://ttlc.intuit.com/questions/1934506-how-do-i-import-my-1099
