CPM stands for Cost per mille viz. Cost per Thousand Impression. You pay when your ad is shown 1000 times. 

CPC stands for Cost per Click. You pay when someone clicks on your ad.

Once the campaign is confirmed, it may take up to 48 hours for the ad to go live. 

Yes. All platforms prioritize Roadblocks over ROS ads and hence in case of such a premium booking, the delivery of your ad will be paused, and the campaign might need to be extended.

Daily impression delivery doesn’t remain constant but can fluctuate by up to 200%.

The clicks shown on the report may not match the actual visits (as per your analytics) to the website as there is usually a significant click to drop off rate. Every click recorded by the advertiser's dashboard does not end up on the landing page which causes this discrepancy.

You can click here to understand in detail the tech reason for the discrepancy in these two numbers.