If you want to put PPC ads on your site, signup for Adsense. If you want to promote your site on other sites on PPC basis, go for Adwords. Visit http://www.google.com/ads/ for more info.
you might want to look into getting kontera ads if possible. it's text based and embedded in the text of your page. some people don't like that it displays a popup over your cursor, but it makes for a clean page