"So the purpose of this action is only to realise the loss?" - Yes. It helps people avoid the perverse situation where they may need to pay a crapload of capital gains tax in one year knowing it's only a matter of time before a company is wound up and they realise a tax loss.
"They dun pay you anything to acqurie the shares from u?" - No. You actually pay them a fee for them to acquire your worthless shares.