OK I need help on how to do this. Instructions say:

state the third congruence that must be given to prove Triangle DEF is congruent to triangle MNO, using the indicated postulate or theorem.

Given: Line DE is congruent to line MN

Angle M is congruent to ANgle D

Method: SAS Congruence Postulate.

I would really appreciate it if you could explain it without it being too confusing. PLease solve it to and explain how you did it. I don't know what to do.