Apple announced plans to infuse the Apple Store with advertisements starting October 5. The Search Ads program entails that users searching for a particular app might see ads for related ones.
The company says that by buying an ad spot, many developers will have the chance to get noticed. App suggestions which are ads will have a distinctive blue badge. The company ensures that the App Store won't be an advertisement minefield, as users will see ads only when it's relevant for them to appear.
Check out the source link for an introductory video by Apple, in which the company explains the nitty-gritty behind the process of setting up an ad for you app.