CPC stands for Cost Per Click, whereas CPM is Cost per Thousand, where the M is coming from? M in Roman numeral for a thousand.
CPM is the cost for a thousand impressions, where an impression It’s a measure of the number of times an ad is seen by a user. In that sense it’s almost like a page view except it only refers to a portion of the page you placed your add.
CPC is how much you will pay per click on your online add.
Which one is better? we can write tons of articles about this, and it is far more complex, for instance, a marketer that would like to see if his or her add is under paid, will want the statistics from the impressions from a particular add.
A person that would like to have a simple strategy, such as just selling a single article, probably would like to pay per click, to see how many people were actually interested on that particular item.
Regardless of what technique you use, the best approach I think is to go out there, post a couple of adds on your product, one with CPC and the other to CPM, and start learning how much the bids are changing on each one, and also.. you’ll see the equilibrium of paying/selling.
There are other variables, such as the position of your add, distribution list, text or image, vocabulary, colors, etc.