Based on your campaign plan, creating brand awareness, increasing traffic, etc., create AdUnits as needed. Each AdUnit allows you to create multiple Ads and allows you to set the show time for each Ad. You can target your Ad to specific target areas on the website. Choose a target area like Guide Selections Target Area, Dynamic Guide Selections Table Target Area, etc.. The charges are different for each target area. A CPM target area will charge based on a 1000 impressions, while a CPI target area will charge per impression, and a PPC target area will charge per click. A target area with CPI will build brand awareness as it will be prominently located and the user will get to see your ad for a number of seconds. A PPC ad is usually shown along with other advertiser's AdUnits, so your Ad text needs to be very relevant and catchy so as to get a click. (See target areas demo here)
Once you have chosen a target area, choose the cost type, fixed or bid. Cost type fixed means, there is one fixed charge for showing the AdUnit, it could be as low as $0.15 or higher. Cost type bid means, others are also bidding on this target area, and AdUnits with the highest bid will be shown. An AdUnit with fixed cost type will have priority over an AdUnit with cost type bid, and will be shown even if there are AdUnits from other advertisers with bids higher than the fixed cost.
Once you have chosen the cost type, a fixed cost type AdUnit will have the cost field populated automatically and is read-only, while a bid cost type allows you to set the bid amt you are willing to pay.
Once you set the cost field, you can now create the text for the AdUnit. An AdUnit can have multiple Ads. Each Ad has a show time in secs allowing the Ad to be shown for that much of time before the second Ad in the AdUnit gets shown, and so on. You can add a title, description, shown URL and click URL to Ad1, set a show time (usually 3 seconds to 5 seconds is very good ), then add text to Ad2 as in Ad1 but with different text and description. You can add text to Ad3 also. You can see a preview of how the AdUnit will look by clicking on the preview button. (See AdUnits demo also for more information).
Save your AdUnit by clicking on Save.