(Source: Schur, p. 83)
John Rawls approached contractualism from his perspective as a political philosopher, and his ideas were rooted in the idea of the social contract as something that all participants of the society agree to follow. The veil of ignorance is one aspect of the social contract and is meant to ensure that every decision is made to benefit all citizens equally without taking into account differences between them.
(Source: Ethics Unwrapped)
The Social Contract (Ethics Unwrapped)
(Source: Ethics Unwrapped)
The Veil of Ignorance (Ethics Unwrapped)