Can I get some help, Im trying to get a better understanding but the video isn't making sense to me, if someone could provide an explanation it would be great! Question:

Below are \triangle ABC△ABCtriangle, A, B, C and \triangle DEF△DEFtriangle, D, E, F. We assume that AB=DEAB=DEA, B, equals, D, E, m\angle A=m\angle Dm∠A=m∠Dm, angle, A, equals, m, angle, D, and m\angle B=m\angle Em∠B=m∠Em, angle, B, equals, m, angle, E.
(The screenshot will explain it better)