You can hover over the stats to see a quick description of what they do (although agility also increases attack speed for hero, I need to add that to the tooltip).
Advice for those doing the harder/nightmare badge: Take lots of risks early on. The "keep fort danger under 10% or else" message is a lie. You always want to defend against a horde, but on non-horde days the only way you can win is if you run 30% risks on your fort. You need as many people out in the city as possible. If you lose, at least it doesn't take you very long to get back to where you were...
You can hover over the stats to see a quick description of what they do (although agility also increases attack speed for hero, I need to add that to the tooltip).