Here are a few links to pictures of step-in harnesses. They vary, of course, in design a bit but the basic idea is the same. The dog "steps" into it with the result being straps around the shoulder blades, under the armpits and a strap across the chest.
Link 1 Link 2 Link 3
Penny's is actually like
this one (with two straps through the chest meeting with the connecting strap. Only her connecting strap is lower so it doesn't come near her neck, just across her chest.
Hope some of these pics have helped!