Many already said how people start dancing. I’ll add some things to keep in mind:

1- culture is a massive factor: nobody mentioned birthday parties. I’m going to presume kids don’t dance at birthday parties in English speaking countries, but elsewhere in the world you have birthdays and I’m going to guess other festivities in other cultures include dancing. That’s a major step before you are old enough to go clubbing. Freestyle in the case of birthdays, but you also need to keep in mind my next point,…

2- TV, Music videos, Videogames and whatever media in which people see these moves also helps people learn them. It’s not uncommon for a small group of friends trying out if they can do this Celebrity Move like in Such Video Clip or whatever and this can happen while they hang out anywhere, even during school breaks.

So yes, if you have the inclination for dancing you have plenty of opportunities to practice and learn as you grow.