You only enter the sales price and the cost. Turbo Tax calculates the gain or loss. The proceeds you got from the sale don't matter.
If you have investment sale losses, after you subtract the losses from your gains you can only deduct up to 3,000 per year. You can only deduct up to 3,000 (1,500 MFS) loss per year after any gains you have. So if you have a lot of current gains you can use up the loss. The rest you will have to carryover until it is used up.
