can anyone help me. i do not understand.

Hello!
Answer:
B. <DEF
Step-by-step explanation:
The vertex is the common endpoint, which is always in the middle of an angle. So E will be in the middle.
Hope this helps!
Answer:
Angle DFE
Step-by-step explanation:
A vertex is a point where two or more curves, lines, or edges meet.
Therefore, it would be the end point.