She's late. Maybe she's not coming ... again. Maybe she hates me. Tugging at his strangling shirt collar, John waited, still standing, at the edge of the picnic blanket. Sweat trickled down back of his neck, tickling, and the smell of the fresh-cut grass choked what little air he could breathe. Then he saw Mary, hurrying toward him with a smile and a picnic basket of her own. Her grin sent his heartbeat banging against his ribs until he thought it would knock him over. She knelt on the blanket, apologizing for her cancellations of their previous dates because of a deadline at work, but who cared about that? She's here, and she wants to be with me. Look at that smile! John knew already that he'd forgiven her.
Maybe not the best example ever, but you'll notice a few key differences in this scene from the ones I presented previously. John is now thinking and reacting to environmental stimuli. I am not telling you that it's hot out and he's nervous. He's just sweating, and you can see it for yourself. You've been given a glimpse into John's head through internal monologue, and through his physical reactions to emotional stresses. These are the hallmarks of deep POV.
Remember that deep POV can get exhausting, just as repetition anywhere in your manuscript can get tiring (or worse, boring). You don't want to overuse deep POV. Save it for the most emotionally charged scenes, or love scenes, if you're a romance writer. Those are the moments when you want that reader-character closeness.
I hope that now, I've helped you understand the levels of point of view a bit more. If not, feel free to drop me a line with your questions. Happy writing!