mark the angles and sides of each pair of triangles to indicate that they are congruent. Triangle BDC is approximately equal to Triangle MLK

If two triangles are congruent the corresponding sides and angles need to be congruent.
Corresponing sides are:
BD and ML
DC and LK
CB and KM
Corresponding angles are:
B and M
D and L
C and K
You mark those corresponding angles and sides as follow: