What you see at the top in light blue and down the right are Pay Per Click ads. On the left and below the light blue area are Search Optimized sites for the specific keyword searched on. As you can see there are only four Search Optimized sites "above the fold", meaning on the first screen without scrolling down. Eight Pay Per Click ads show.
Search engine optimization can successfully get your site to the top after careful work on 2-3 keywords per page. Pay Per Click has an unlimited number of keywords that you can add. Look at the results above for the keyword phrase "lawn mower parts". In copy on a page, your might use "lawn mower parts" as your keyword phrase, but you would not use "lawnmower parts" along with it, so you would miss out on nearly 1300 searches a day. In a Pay per Click campaign, you could use both and be found in either spelling.
What you see at the top in light blue and down the right are Pay Per Click ads. On the left and below the light blue area are 