If a transversal cuts two parallel lines, then the alternate interior angles formed are congruent. When a transversal cuts two lines, the pairs of angles on either side of the transversal and outside the two lines are called the alternate exterior angles. The students gain knowledge about steps followed in the construction of parallel lines and to find the distance between them. It also helps students understand other concepts like transversals, angles made by a transversal and relations between angles. Two lines which lie in the same plane and do not intersect when produced indefinitely are called parallel lines. It includes fundamental geometrical concepts like parallel lines, properties of parallel lines and transversal lines.