There are 2 ways to ride a skateboard: regular and goofy. When you are first learning to skateboard, try skateboarding both ways. One way will feel a little more natural and that stance is the one you will use for all of your skateboard tricks (until you learn to skate switch, but don't worry about that just yet).
Stance just refers to which feet are positioned on the board. Just like some people write with their right hand, some people write with their left. We know that most people write with their right hand rather than their left, but when it comes to stance the numbers are more even. There is no right or wrong stance. It comes down to personal preference and what feels more comfortable. The best way of finding out your stance is to just go outside and ride both ways and see what feels better. Typically one way will feel more natural. It can be frustrating at first, especially if you don't have someone to help you; However, the following should help you determine your stance.
Someone who skates regular has their left foot on the board, while their right foot pushes
Someone who skates goofy has their right foot on the board, while their left foot pushes
How to Determine Your Stance:
The best way to determine you stance is to just ride and see what feels more comfortable. However, some people have a hard time deciding what feels best.
1) Shove Test
This is the best technique to help determine your stance. Have a friend stand behind you and give you a little push when you don't expect it. The foot that you first put forward should be the foot that will be on the skateboard. The foot you put forward is your stabilizing foot, so you want your stable foot on the skateboard. Be careful when doing this. Make sure the person being pushed will not be in harm's way.
2) Kick Test
Grab a football or soccer ball and try to keep the ball in the air by kicking it up with one foot. Try both feet at different times and see which foot can keep the ball in the air longer. This foot should be your kicking foot. Ex. You can keep the ball in the air on average five times with your left, and three with your right. Since you are kicking with that foot, have that foot push on a skateboard. In this example, you are goofy footed.