It is same as domain trading, and is also a popular business to earn money online. However, in this method, unlike domain trading, you do not deal in domains but in websites.

Create a website, and work on it for 3-6 months or more until you start earning money from that website. After earning for 2-3 months, you can put that site on auction on Flippa.com or other websites performing such options. You can easily sell it on 15-20 times more than you earn monthly from that website.