Okay, you are given that angle 1 is congruent to angle 4 and angle 2 is congruent to angle 3 (you should say that in the proof). Angle 1 is congruent to angle 2 by "VOA" (vertical angles) so all of angles 1, 2, 3, and 4 are congruent to one another. To prove that AC is parallel to BD, you need to show that angle 4 is congruent to angle 6 or that angle 5 is congruent to angle 3 (alternate interior angles).