Your total cost is based on publisher price per 1000 views. The decision where to place your ad is made by you. You can cancel or stop your ad anytime if unhappy with the results or increase it to get more clicks if you see it is working well.
Placing ad is very easy. Just create attractive banner, choose right category and one or more website. Always check CTR, CPM stats. Tip: sometimes smaller and cheaper website will give you better value than large and popular website.