Apps have grown in popularity over the last decade and more and more apps are hitting the market that are free. Free apps can be great but often they are covered in adverts and the only way to remove them, is to upgrade to the full version.
If you are in the process of having an app made then you need to decide as to where you are going to have ads on it. If the app is going to be free but you need to be able to make some money from it, then you will need to show ads or in app purchases. Adverts within apps often have a low success rate and can actually put people off using the app if the ads are appearing too often or hard to close.
The best way to integrate adverts in to your app is to do it more discretely and to make the ads relevant. Advertising products or services that are linked to your business may increase your chances of someone clicking through, and rather than making it a big stand out banner, often a clickable link within a description can work better in terms of conversions.