Ads are set within the ad groups just like keywords are. The ads must be relevant to the keywords you’ve set. You should always have a few different ads within an ad group to see which ad performs best for your keywords. Whether it’s text only or image ads, it is good practice to have at least 3 different ads to start off with. You can add more if you like but don’t add too many. The ads that have the highest click-through rate (CTR) should be keepers and those who perform poorly should be disabled and removed.