If you have done a same-day sale, all of the income and tax withholdings should be reported on your Form W-2 Wage and Tax Statement. You should not have to report any gain or tax withholdings elsewhere on your return. You will want to verify with your employer that this information has been accounted for correctly on your W-2.
If, however, you received a federal Form 1099-B Proceeds From Broker and Barter Exchange Transactions, you will need to report this transaction on your return since the IRS also receives a copy and will be looking for the information on your return. You will need to ensure your basis is reported correctly on Form 1099-B based upon your records. If your basis was NOT reported correctly then you will need to add an adjustment code and amount to account for this difference.
To enter Form 1099-B for your capital gain or loss transactions into the program:
Your basis in the stock will need to match the sale proceeds in order to not report a gain or loss.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.