1. An intersection is where two or more roads meet
An intersection can be the classic cross, a "T", a "Y" or even "box". Traffic circles or Roundabouts are considered intersections as are diagonal intersections that form more of an "X". On-ramps and off-ramps are not considered intersections. Note that an entrance to a "Jug handle" would not be considered an intersection, but jug handles usuakky end in intersections, so take note ; )
2. A motorcycle approaching an intersection counts
If you are approaching an intersection and a motorcycle is also, that's three points. However, if you have passed beyond an intersection and you spot a motorcycle approaching the intersection you just passed, that doesn't count as three points, just one.
3. A motorcycle stopped at an intersection counts.
Just as with approaching an intersection, a motorcycle stopped at an intersection counts for three points as well. Additionally, if you are stopped at an intersection all motorcycles that run through it are worth three points. Clearly intersections are the best place to gain points!
4. Beyond an intersection does not count.
If you have passed an intersection and then spot a motorcycle it only counts as one point. If a motorcycle has passed an intersection and you are approaching the same intersection it passed it only counts as one point. The three point modifier for intersections only applies while approaching or in an intersection.
In general, if you or the motorcycle have not yet passed the intersection it's a three pointer. If either of you have passed the intersection it is a one pointer.