You just arrived here so I guess it's expected that you're unfamiliar with what a holodeck is. Basically, it's a room that creates artificial environments using hard-light holograms. Everything created inside the holodeck will look and feel real, but in reality are all illusions. Think of it like a video game being brought to life in the real world.

[Hopefully, his explanation helped her understand how amazing the holodeck is.]

This is why it's the perfect place to train in. We're going to use it to simulate an entire skate park.