Drafting means staying inside the slipstream of the car(s) ahead of you. I think the announcers and the in-car cameras on the Sunday race did a pretty good job of illustrating the effect of drafting on tactics and the basics of how it works.
When you’re the car in the lead, driving 160-200 miles per hour at various points around the track, your biggest impediment is air resistance. (Assuming you don’t hit anything solid, that is.) This would be a bad thing at first consideration, but your car is designed to use this air resistance and transfer it into a force that presses you to the racetrack, creating more friction at the places where your tires meet the road, and thus giving you more maneuverability. Unfortunately, this maneuverability comes at a decrease in fuel efficiency.
Now, when you’re not the lead car, which is more often the case for any driver (even Gordon), you have a choice: either use the slipstream to increase your fuel efficiency, or abandon it to increase your maneuverability.
If you draft (stay in the slipstream) then you run the risk of not being maneuverable enough to stay on the best course around the track at the speeds at which the leader is travelling. The car ahead of you can do it, because he’s got better tire friction. However, you are using less gas to go the same speed, and so presumably the lead car will need to pit sooner than you. You can drop back some to “grab” more air, but to win you’re going to have to pass the guy ahead of you.
This is where drafting and air resistance make the sport interesting. When you come out of the leader’s slipstream to pass him, it’s like your car is suddenly hit by a wall, and you’re pressed to the ground more. If your aerodynamic surfaces aren’t precisely balanced (and they intentionally aren’t), then you’re also going to feel a sideways force. Typically this force is to the left, to help you maneuver the turns. And since you’re also experiencing more drag, you need to be able to increase the throttle to compensate for it - more than compensate, since you’re trying to pass.
All of these factors dictate the kinds of tactics used on a super speedway like Daytona and Chicagoland. It’s surprisingly a lot more like Grand Prix tactics than you’d think - you need to stay on the tail of the guy ahead of you and wait for him to make a mistake. Sometimes, if you’re right on his tail, you can psyche him out and increase the chance he’ll screw up and give you the opportunity to take the best line around a curve and pass him. Or you can try and pass on a straightaway and hope you’re not out of the groove when you get to the next turn. And if you’re in second position, then it may be a good idea to let the car ahead of you lead until the end of the race, because maybe you don’t have the fuel to lead the rest of the race, and it would be disasterous to take the lead too early - you’d just have to pit right at the end of the race.
It looks like a simple sport, but it isn’t. It’s very subtle. And it takes a lot of stamina to drive those cars, and a lot of engineering and physics to build and race them.
I think the more interesting thing about this weekend’s races was the effect that the new track surface had on the race. Lots of unexplained tire damage, a really narrow groove, and the resulting hazards from the unconditioned surfaces on the high parts of the turns. After Saturday’s incidents, I’m surprised there weren’t more on Sunday.