Club wars - Feedback

The tutorial was not thorough enough, and neither were the videos I found on YouTube. I'm now getting contest challenges that I don't understand. For example, what's the difference between "Collect War Items" and "Do War Deliveries"? On the War Supplies window, it says "complete war deliveries to get war items". So If I get the desired regular items and pack them I get a reward of a war item. It seems that the process is completing a war delivery, and the result is collecting war items. So is this two ways of saying exactly the same thing? I get how to "launch attacks in club wars", but not "shield opponents from attacks". I know that if a city is hit hard enough it will be shielded. Can a city shield itself? Can we shield a city without attacking? Can I attack a city someone else has attacked and get credit for it when that city's shield goes up? How many times to I need to launch an attack on a city before its shield goes up? I wouldn't have a problem gradually learning these things by trial and error, but these are contest challenges that I have to do right now and there's no explanation. Help!