The difference between goofy and regular is, if you're goofy-footed, your front foot is going to be your right foot and if you're regular, you're front foot is going to be your left foot. Some people like to transition while they're pushing. It's called skogging, so skate-jogging, which is a little weird, it's a little kooky. Some people like to do it if they're pushing long distances, but each to their own. Now, there's something else people don't generally respect.
Those are mongo pushers. That's when your standing foot is in the back and your push foot is in the front. Same thing if you're goofy, goofy foot in the back, pushing with your left foot. It's a little weird, some people like it. I suggest that you pick one position, you stick with it. Front foot should generally always be in the front. Now, if you feel more comfortable with one foot over the other, just go with it, stick with it. If you want to be bidextrous with you feet, you can do that, too. It's going to be a little more confusing for you at the beginning, though. And that's how you know whether you're goofy- or regular-footed.