Theory:

Two angles and the included side of a triangle are equal to two corresponding angles and the included side of another triangle, and then the triangles are congruent.
Suppose the two angles of the first triangle are \(a\) degree and \(b\) degree and the included side is \(x\) units which are congruent to the second triangle whose angles should be the same \(a\) degree and \(b\) degree with the included side \(x\) units.
Example:
Theory_1.png
In here the two angles of the first triangle are \(40°\) and \(60°\) units, and the included side is \(8\) units which are congruent to the second triangle whose angles are the same \(40°\) and \(60°\) with the included side \(8\) units.
Important!
ASA stands for "angle, side, angle" and means that we have two triangles with two angles and one side are equal.