Angles 4 and 5 are corresponding; this means that they are sitting in the same places within their angle "bunch" for lack of a better word. We are then told that they are are congruent which means that they have the exact same measure. Corresponding angles can exist without being congruent, but because they are, that means that A and B HAVE to be parallel. So true.
When two lines are parallel, the corresponding angles formed by the transversal (intersecting line) are congruent. This is called the corresponding angles postulate. It can be used in reverse: if two corresponding angles are congruent, then the non-transversal lines are parallel.
