Theory:

Let us try placing A4 sheets precisely on top of each other. What happens to that set of A4 sheets?
 
The second sheet of paper completely covers the first sheet of paper. It happens as the dimensions of the A4 sheets are precisely the same.
 
The property of two or more objects having the exact dimension is called congruence. The objects that exhibit congruence are called congruent figures.
Example:
Let us look at a few examples that exhibit congruence.
 
1. Two triangles with the exact dimensions.
 
1.svg
 
2. Two screws with the same shape but placed in different directions.
 
screw-4737202_1920.png
In the following sections, we will deal with congruence in triangles elaborately.