This means that, in order to prove that the triangles are congruent, they must have two congruent sides with the angle between them to the same.
We know that sides AB, ED, AC, and DF are all congruent as they all have a single mark through them. From this, you can conclude that the triangles already share two sides. All we need now is the angles in between to be congruent. This means that angle A and angle D need to be congruent.
