Your skateboard stance is the way you stand on a skateboard. Leading with your right foot or your left foot.
Regular foot riders place their left foot in the front while skateboarding.
Goofy foot riders place their right foot in front while riding.
Some people say that more riders skate with their left foot than their right. So that is why it is called regular. I have not found this to be the case. Goofy vs Regular seems pretty evenly divided across the skaters I have seen in the last twenty years.
The way to find your stance is to pretend you are going to slide on an icy puddle. Take a few steps and jump. The foot you use to lead with will determine your stance.
Use the foot you lead with when taking the stairs.
Some use the kick test.
Which foot do you use to kick a ball?
No matter which way you go; goofy or regular. Try to switch it up a few times and see which feels better.
I am a goofy foot rider so naturally I like that best. If you skate your opposite way that is called switchstance or switch. This is more advanced. Doing tricks switch starts to separate the good skaters from the rest.
I learned to skate switch a little out of boredom and a little out of wanting to skate spots both ways.
I like to skate switch. It's fun.
Now you know what skate stance is and how to find out what yours. get out and skate up a storm.