so much to learn

Despite having a few half marathons under my belt and a plethora of 5Ks, I really have no idea what I'm doing. I feel like a newbie because I've never actually followed a training plan before. Today, my training plans said "30 min tempo." Um, sure, ok. (But what is a tempo run, really?) So, I've been exploring, learning, and researching. "Comfortably hard." I was nervous. What is "comfortably hard" to me? The traditional answer to a tempo run seems to be 10 min warm-up, 20 min at a magical "comfortably hard" pace, followed by a cool down. After some reviewing suggested paces on the McMillian calculator, I decided to aim for a pace in the 8:40s for two straight miles. I kept my middle two miles around a 6.9-7.0, and you know, it wasn't bad at all. It's now 14 hours later, and I feel great. My legs feel fine, fresh really, and not fatigued at all. So, this leads me to a whole other topic that I need to explore: What am I really capable of? Am I pushing myself hard enough? Can I take it to the next level?