By definition:
Congruent figures in geometry are identical in shape and size.
This means that two figures are congruent with each other even if they are rotated, flipped or trasnlated as long as they have the identical shape and size.
For example, look at the following picture
We notice that the triangle has the same size and shaped, hence they are congruent. Furthermore we can say that the side BC is congruent to the side ZY and so on.