Taking the road analogy, you can have things like traffic lights which switch between roads on a junction, giving each one a chance to access the junction in turn, but apply equally to all types of traffic on that road. That's net neutrality. You could also have things like bus lanes which give one type of traffic, buses, priority over other types of traffic. That's not net neutrality.
Today, when driving home, I was delayed for about 20 minutes because a lorry ignored a "no HGVs" sign and went down a narrow road towards a single track bridge that it couldn't get across, when it should have gone about 3 miles upstream to the next bridge. That is an example of where net neutrality would be a bad thing.