The scammer will usually be after your bank account details so they can steal your money. Sometimes, they will actually send you money and let you keep a commission. The money they send to you will either be from someone else they have scammed, or from some other illegal activity.
The scammers want you to transfer or ‘launder’ this ‘dirty’ money so that you are the one who will be tracked down by the authorities following the money trail from the crime that generated the dirty money.
The scammers may ask you to transfer the money by wire (e.g. by using Western Union). Sending money this way means it is very hard to trace where the money ends up. So when the police come knocking on your door, the money trail would end with you! Money laundering is a serious crime—you should ignore any offers that require you to transfer money for someone else.
If you have seen emails like this: watch out! They are a scam and will give you nothing but dirty tricks and dirty money. You should never provide your banking or personal details to anybody you don’t know and trust. Do not follow any links in the email or reply to the email: just delete it.