My rear brake rubs after I fixed a flat on my Northwind Commuter 5. What should I check?

Make sure the wheel is fully seated in the dropouts: loosen the axle nuts, push the wheel all the way up into the slots, then retighten with the bike on the ground and spin it. If it still rubs, loosen the two bolts that hold the brake caliper to the frame, squeeze the rear brake lever and hold it to center the caliper on the rotor, then tighten the two bolts while still holding the lever.