The click-through rate (CTR) is the number of clicks your charity's Google ad receives, divided by the number of times the ad has been shown (known as impressions).
CTR is a good way of measuring the success of your charity's ads and keywords. A high CTR for a particular ad indicates that your ad is doing a good job of selling your charity. A high CTR for a keyword shows that your charity's website is of interest to web surfers searching for that keyword.
You should care about CTR because it can save you money.
Google decides how high up to display your Google ad by multiplying its "Quality Score" by the price you are willing to pay for a click. So if you want to be placed high on the page (where more people will see it), you either have to pay more money or increase your Quality Score. Google's Quality Score is determined by a combination of CTR, the relevance of the ad, historical keyword performance and other relevance factors.
So, by having a better CTR (or a more relevant ad) your charity's ad will be placed higher in the Google search results page without any additional cost.