What is the difference between a box and a rail?

A box is wide and provides plenty of surface to slide on. A rail is narrow, like a metal bar. You ride them similarly, but rails require more precision and body tension. That is why we always start with boxes. Once you can slide them confidently, we introduce simple rails, often low and rounded. The goal is to jump onto the rail confidently and slide with flat skis. With practice, it works as you learn step by step.