CPA Stands for "Cost Per Action"
Cost per acquisition (CPA), also known as "Cost per action" or pay per acquisition (PPA) and cost per conversion, is an https://en.wikipedia.org/wiki/Online_advertising pricing model where the advertiser pays for a specified acquisition - for example a sale, click, or form submit (e.g., contact request, newsletter sign up, registration etc.)
Formula to calculate cost per acquisition
Cost per acquisition (CPA) is calculated as: cost divided by the number of acquisitions. So for example, if one spends £150 on a campaign and gets 10 "acquisitions" this would give a cost per acquisition of £15
PPC Stands for "Pay per Click"
You Simple Pay Per Click made to your Ads.
Source : Wikipedia https://en.wikipedia.org/wiki/Cost_per_action