The RayCast action does a raycast from the start to the end entity.
ray_class: That's the class used to do the ray cast, which can be used by Enter/LeaveRayHit to filter which ray cast we're interested in.
ray_start_entity: The entity the ray start's from. If empty we'll use the action's parent entity as the source.
ray_end_entity: Is the target where the ray ends. If empty we'll use the action's parent entity's forward direction and max_distance to define the target. The forward direction is the Z-axis (blue arrow in the transform gizmo in local space)
max_distance: When using the start entity's direction this is the maximum distance from the starting position of the ray.