As a Line Segment is just an straight line and doesn't include any curved area inside it, it has no Fill.
Lines do have a stroke. Let's increase the Stroke to 20 points. Shown in next slide.
Click on the Stroke to open Stroke panel or you can open it from Window menu. Stroke Panel has various options including Weight, Cap, Corner, Align Stroke, Dashed Line, Arrowheads and Profile etc. These are discussed one by one in coming slides.
There are 3 types of Cap for Line Segments.
Dashed Line is used to create, obviously Dashes in the Stroke of the line. In the Dash option, we can define the length of Dash as well as the length of Gap. In doing so, we can create a pattern of 3 different lengths of Dash and Gap.
There are 2 Arrowheads, one for Start Point and the other for End Point. Start Point is the point from where we start creating our line. End Point is the end where we finish creating our line.
Scale option control the size of Arrowheads in the line.
Align options aligns the Arrowhead before or after the anchor points.
Width Profile of the Line Segment is the variable profile for width of stroke. Various width profiles available are shown below.