Skew lines are lines that are not on the same plane (therefore they will never intersect), but are not parallel. For example, visualize a line drawn from east to west on the floor. Now visualize drawing a diagonal line on the ceiling. Those lines are not parallel to
each other, but they would never intersect either. Keep that visual image in your head as you do this problem
This is just some basic principles of reading off info from the equation of a line. You learned how to get the sine of the angle between two vectors in Lesson 9. Note that the vector PQ forms the hypotenuse of a right triangle, and the side of the right triangle that is parallel to the normal vector you
found earlier, is the distance between the two lines.
You can use trigonometry to find that distance (that is why they had you find the sine of that angle earlier), or you can also use the projection vector formula I taught you in Lesson 9. Find the projection of PQ onto n. The length of that projection vector is the distance you seek.
Your course notes also
give you a formula for finding the distance between a point and a line that can also be used here, too, if you wish, but, they have pretty much guided you through all of that formula in the previous parts of the question.