Since the areas are huge, (grass type doesn't matter) I would take plugs from your healthy areas of grass to put into the bare areas. If you have a tiller, just go over the bare areas with the tiller set at a shallow depth to loosen the soil. If you don't have a tiller, you could scratch it up with an iron rake. If you have a plugger, great, if not you can just take a good sharp knife and cut out small plugs from your healthy grass (shape doesn't matter), place them in your bare areas several inches to a foot apart, gently step on them to ensure good soil contact, water and wait. Of course, don't take all your plugs from the same area--jump around so you won't just create another trouble spot. The little places you take the plugs from will quickly fill back in and when your plugs take root, they will fill in your bare areas much more quickly than if you wait for it to come in from the edges. If you don't get sufficient rain while the plugs are trying to root, continue to keep them watered. And don't feel like you are asking dumb questions--we all have to learn and that's a big part of what this forum is about! We love helping each other :)