Part - 1
It is a Vector Software
which uses Mathematical Shapes to draw on the Canvas.
What is Vector?
Vector is a quantity having a direction as well as magnitude especially as determining the position of one point in space relative to another.
These are Computer Graphics which are defined in terms of 2 dimensional points (or anchor points).
Points (or anchor points) are connected to one another by lines and curves (also known as path or edge) to form various geometrical shapes like rectangle, ellipse (circle or oval) & polygons etc.
All of these points have a definite position on the x-axis and y-axis of the Art Board or Canvas or Work Plane. Hence determines the direction of the path.
These path may have different properties values such as stroke color, shape, curve, thickness (or stroke weight) and fill.
Most used file formats or extensions for Vector Graphics are SVG, EPS, PDF, CDR or AI.
For Full information read linked blog.
Line Segment Tool
line segment tool in adobe illustrator
Properties of line segment tool
Top nature photography for mobile wallpaper