I'm a bit confused with question 4. An intersection is when two things intersect at one point, so it can't be just one line intersecting. But then I'm confused on how the parameter (0.2 and 1.1) affects this.
Great question. The segment AB is part of the line AB, the part between those two points.
In computer graphics, we often care about line segments, as opposed to lines.
Suppose A=(1,0,0), B=(2,0,0) and C=(3,0,0)
The segments AB, BC and AC are all part of the x-axis, but they are different segments and might or might not intersect the same other lines.