Linear perspective is a system for translating 3D space into two dimensions. The system is based on scientific study from the 17th century and is intended to create the illusion of 3D space.
While illusion may not be a specific objective of drawing, understanding how linear perspective works has various useful applications.
Basic elements of linear perspective:
1)

Determine your eye level (some times referred to as the horizon line) 
2)

Vertical lines stay vertical

3)

Line that we consider horizontalparallel to the groundconverge at vanishing points on our eye level.

Parallel lines of parallel planes converge at the same vanishing point. 