Explanation:
ASA stands for angle, side, angle
How is triangle ABC congruent to DEF
If any two angles and the side included between the angles of one triangle are equivalent to the corresponding two angles and side included between the angles of the second triangle, then the two triangles are said to be congruent by ASA rule.
In the diagram you shared, side BC is equivalent to line FD
Angle B = angle F
Angle C = Angle D
(Compare the markings on both triangles)
The relationship between triangle ABC and triangle DEF are congruent only by 2 angles and one side.