Yes, the 1099-B form will be reporting the gains and losses that occurred at the time the stocks were sold and that information does have to be reported on your tax return. Even though you were already taxed on the dividends received, you now will be taxed on the net of any gains and losses that occurred on the sale. For long term capital gains (when the stocks were held more than one year), the tax rate is typically at a lower rate than the rest of your income will be taxed upon.
Below are steps for where to enter the 1099-B form into TurboTax:
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