Theory:

Two sides and the included angle of one triangle are equal to the corresponding sides and angle of another triangle, and then the triangles are congruent.
Suppose the two sides of the first triangle are \(x\) units and \(y\) units and the included angle is \(p\) degree which is congruent to the second triangle whose sides should be the same \(x\) units and \(y\) units with the included angle \(p\) degree.
Example:
Theory_1.1_2.png
 
In here the two sides of the first triangle are \(3\) units and \(7\) units, and the included angle is \(40°\) which is congruent to the second triangle whose sides are the same \(3\) units and \(7\) units with the included angle \(40°\).
Important!
SAS stands for "side, angle, side" and means that we have two triangles with two sides and one angle are equal.