"S" stands for "side" and "A" stands for "angle"
SAS = side angle side
The order is important because the angles must be between the two congruent sides.
One pair of congruent sides is AC = CE as shown by the single tickmarks.
The other pair of congruent sides is BC = CD shown by the double tickmarks
The congruent angles are the vertical angles BCA and DCE. Vertical angles are always congruent. Note how these angles are sandwiched between the tickmarked sides.
