So can the DM just kill you? No, not really. Can the DM decide that lightning strikes at you because you wouldn't take the hint and get off the roof in a storm while wearing your full plate armor? Yes, but but there's a skill check for for that...
edit: does that make any sense?
I was really being overly dramatic.
But Iron Chic provides a great example. Think of it kind of like real life. If you were going to cut a tree down in your yard, what would be the process? Well me personally, I would assess the difficulty (rolling for initiative or dexterity) and whether I was capable of such a feat or not. Now most of us don't walk around with a little felt bag of multi-faced die to determine our actions in daily real life. (Believe me - there are those that do ) We use our brain to do virtual dice rolls to determine what we are going to do today....The same in the game. Since in game, there is no automatic way to know about things except to explore them, we used dice in relation to things you would normally do in real life without thinking. The example I think was given: If you want to scale a wall, you would roll for initiative, dexterity, etc
Now that I have made it more confusing.... 
For real guys, you all will be fine I think. I believe there are enough people who have played some amount at some point in their life that they will be able to help others...remember you are not competing against each other per se. For the most part you will be waiting on me as I will be your weakest link until I get a few sessions under my belt and get my DM aura back. So I will be the inept one in the mix...but I think you guys will be fine.
I really was just being overly dramatic...