REDDRAGON, here is a brief answer to give you some idea.
CPA requires some type of action to be taken before you earn a commission. The action might be for a person to sign up to receive something. That something might even be something that is free. The action might be having the customer furnish information about themselves which provides a lead. That action might be the purchase of something. A specific action is requied and must be met.
CPC is where you are paid per click, such as with AdSense. If a person clicks on an ad, you earn some money. The amount can vary.
CPM pays a certain amount, usually based on a certain amount per thousand impressions. In most cases, but not all, a person will earn less with CPM than they will with CPA or CPC. But there are some sites which can't get accepted into any CPA program or CPC program and must settle for CPM. There are others that just don't perform well will CPA or CPC and their best chance is with CPM.
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