I am planning to sale custom websites. I have people to work on them and everything I need to start. But I don't know how to advertise and how to find the customers? Any sugestions please

Start simple. Submit to all the free search engines. e.g. Google. Go around these forums and start telling people about your site maybe. You can advertise on this forum too. Then depending on how much money you have, you can do different types of search engine advertising. Check out google for their advertising. Very inexpensive and easy to use.

How can I make money just of the websites? How do the most people on this forum make money?

Well, some of them just wait for somebody to make an offer for a job, then that's your chance to take it and offer them a good price and good service.

Finding web design CLIENTS is not that easy. There's some work to be done in helping them find YOU. Get listed in some of the free directories out there. Do a Google search for "web design directory" and things will popup. These free listings will help get some visitors to your site. Then if they inquire about your services, you go from there.