Triangles which are exactly the same shape and size are congruent.
Note: this also applies to shapes other than triangles.
Triangles are congruent for the following reasons:
Three matching sides (SSS)
Two matching sides and the angle between them (SAS)
Two matching angles and a corresponding side (AAS)
In a right-angled triangle, the hypotenuse and one matching side (RHS)
Now it's over to you. You will identify congruent triangles and give reasons as to why they are in fact, congruent.