Let's just try listing all the forces that are present (regardless of what they are actually doing). Then draw a free body diagram to figure out in which direction they point in.
The centripetal force makes sure that these riders don't go spinning off in space. What keeps people in the same place? (Horizontally)
If people aren't moving vertically (otherwise they'll splatter their brains all over the floor!) What forces are present in the vertical direction? What keeps them up? What makes them fall?
Tension isn't present in this problem. Tension usually has to do with strings. Keep in mind that a normal force is always perpendicular to the hard surface.