Form 8949 is a new form for reporting capital gains introduced in the 2011 tax year. On Form 8949 you must list transactions that in previous years would have been listed on Schedule D [Capital Gains and Losses] or Schedule D-1 [Continuation Sheet for Schedule D], which has been discontinued. Note that you still must file Schedule D, only now it sums up the transactions listed on Form 8949.
The transactions you must report on Form 8949 include
sales and exchanges of capital assets
gains from involuntary conversions of capital assets not held for business or profit
nonbusiness bad debts
Potentially, your tax situation could require three separate Form 8949s, as an individual form must be submitted listing all
short-term transactions reported on Form 1099-B with basis reported to the IRS
short-term transactions reported on Form 1099-B but with basis not reported to the IRS
short-term transactions that do not fit into either of the first two categories
You will receive a Form 1099-B [Proceeds from Broker and Barter Exchange Transactions] from your broker if you sold a covered security during the tax year.