What Is a Step-in Dog Harness?
The term “step-in dog harness” refers to any dog harness that goes on from the bottom upward -- in other words feet go in first, and it fastens at your dog's back. There are various styles of step-in harnesses, including webbing strap harnesses and vest-style harnesses. A big advantage to a step-in harness is that any pressure from the leash is spread across your dog’s chest and shoulders, rather than pressing on the neck or trachea as a collar will do.
Put the harness flat on the ground. Have your dog lift one front paw at a time, and place the paw through the corresponding leg hole of the harness. Once both front paws are in, pull the harness all the way up your dog's body and fasten it at your dog's back. Then adjust it so it’s not too tight (you should be able to fit two fingers between the dog’s body and the harness.)
They aren't necessarily better, just different. Some dogs may find step-in harnesses harder to get on (for instance, seniors with stiff joints or super wiggly pooches that won’t stand still), whereas others prefer step-in harnesses to those that go over the head.
Not all step-in harnesses are no-pull harnesses, but yes, you can buy step-in harnesses with no-pull features such as front leash attachment clips.