In forms mode you cannot enter investment sales directly on Form 8949 or Schedule D. Individual sales have to be entered on a Capital Asset Sales Worksheet. From there the information flows to the Form 1099-B Worksheet, and then to Form 8949 and Schedule D.
Entering investment sales in forms mode is very complicated and error-prone. That's why TurboTax strongly recommends using the Step-by-Step interview to enter investment sales, as Critter-3 said.
