If the light has raytraced shadows on, rays will be emitted from the light source aswell, to see where shadows are cast. If an object is transparent the ray passes through, according to how transparent a surface is. However, the ray continues its straight path and adds the remaining color of the first object to the second or third one it hits. If a refraction index is set, the rays path will be altered and it keeps going in a slightly different direction. Like when light passes through another medium as it does from air to water.
Reflection maps are fake reflections, handeled as textures.
As we can see, there s basically two ways of travelling rays. Straight and not-straight. Also, at certain occasions the ray can be splitted into two or more rays that shoot in different directions. That happens for example when a partly transparent object is reflective at the same time or has refraction aswell. It can be set how many rays XSI will handle at the same time and when they stop bouncing around, from reflection to reflection.