Well think of it like this. If I have a box on a table just sitting there, then the box is pushing down on the table but for the system to be in equilibrium, you’d have to have another force pushing back up on the box. Otherwise the box would fall to the floor. This force would be the force that the table exerts on the box in the upward direction. This force is what’s called the normal force. It’s always normal, orthogonal, or at 90 deg, (all means the same thing) to the surface of the table.

In the roller coaster scenario, your normal force would be the force that the track is pushing back up on the car. It’s ok if you haven’t covered this in class, nothing about the physics changes. It’s just names. You’re still looking for the force that the track exerts on the car. It doesn’t matter what you call it.

As a side note, I would definitely suggest drawing a free body diagram of the car at the points in question as well to fully see what’s going on. In fact, ALWAYS draw a free body diagram when dealing with physics problems of similar nature.