I don't know that you have purchased or not domain. Everything is depend on your business, Aim, Your interesting and more that you want to set goal. make a websites according your interesting and then think earning resourcing.
You probably menat kind of adverts displaying systems on parked domain right ? This is possible but for fresh domains you will earn nothing, if you have PR domain with some BL and traffic you can get good income.
You can either; - Park it and make money off of third party ads (need traffic though) - Turn it into a website (affiliate sales, blog, forum etc.) and make money of off sales, advertising, etc. - Sell it Just a few of the top . . .
There are so many ways to earn money for paid domain. The most important is visitor. If you get a minimum 1.000 unique visitors per day (from search engine), the advertisers will come to you....believe it. So SEO and Link Building/development is your concern after you buy a domain.
Well the domain must be a good domain to make money with that! You can use domain parking, your own ads or try to sell...