To bring a discrimination case, you must prove that the employment action (firing, reduced hours, skipped for promotions, etc.) was taken specifically because of your sex, race, national origin, religion or age.
You can prove this by demonstrating that:
You were treated differently than someone of a different sex, race, national origin, religion or age.
Someone who is very similar to you in position, rank, or job duties, and who is of a different sex, race, etc., was treated more favorable under similar circumstances.
That there was no legitimate, nondiscriminatory reason why the employer treated you differently.