When two figures are congruent they will have exactly the same sides and exactly the same angles.
Figure in the left side can be converted to figure to the right side by using the following transformations
1) Move the figure by 1 towards left side.
2) Move the figure by 1 towards down side.
3) Take time image of the figure taking y-axis as a mirror
as we can see that there is no dilation in sides of the figure hence both the figures are congruent.