You send 0.6 BTC to Address B. Your change 0.4 BTC will be sent back to change address (address C) in your wallet.
If you spend the coins or part of the coins you sent to address B and increase the fee in a way that it can make two transactions to be confirmed, because of that, miners will include your transaction into a block and it would be confirmed after the block is mined.
Instead of using 0.6 BTC or part of the 0.6 BTC in address B, you can use 0.4 BTC or part of the 0.4 BTC in address C to achieve the same result. It is called child-pay-for-patent.
Ok bro, thanks!!!