Consider the diagram.

Parallel lines r and s are cut by transversal q. On line r where it intersects line q, 4 angles are created. Labeled clockwise, from uppercase left, the angles are: 2, 4, 3, 1. On line s where it intersects line q, 4 angles are created. Labeled clockwise, from uppercase left, the angles are: 6, 8, 7, 5.

Given that r||s and q is a transversal, we know that by the [].

corresponding angles theorem
alternate interior angles theorem
vertical angles theorem
alternate exterior angles theorem