What do mean by set-off and carry forward of losses?

set-off. Capital gains and losses will OFFSET each other on the schedule D of the 1040 tax form. That would mean that that the loss would be subtracted from the gain reducing the amount of the gain for the tax year.

And if you have any remaining loss after completing the schedule D correctly that amount of loss up to the 3000 maximum amount would be used to OFFSET (set-off) (subtract) from your ordinary income amount on your 1040 income tax return reducing your total income and also will reduce your taxable income and will also reduce your federal income tax liability on your federal income tax return.