They send you an e-mail to your GMail.com account that falls by default in the SPAM folder. The subject section of the e-mail has your password in it. The correct password. In the body of the message, the extortionist says in so many words they know and have software that tracked you on adult websites and in so many more words, it says to the effect that they "turned your PC monitor into a webcam using special software," while you were viewing pornographic videos.
They demand Bitcoin money toward the bottom of the e-mail and says that you shouldn't even think about contacting law enforcement. They mention also in so many words that once they receive the Bitcoin ransom money, they'll go away like this never happened and none of your email contacts will ever see secret videos of you at your computer.
This is a SCAM. Don't fall for it.