How does CPM work ? How it is useful

If you click on an ad on someone else's site, they will be paid based on their MWR arrangement with the company that is offering the ad. The MWR is most wanted response. So some ads have an arrangement where you get paid when someone actually buys a product. Others have an arrangement where you get paid when someone signs up for a subscription, service, newsletter, free trial or performs some other action on the advertiser's site.