Can someone please EXPLAIN this to me, I really need a explanation not just a answer.

First line:
XV, XT, VT
Second line:
YV, YU, VU
Notice:
[tex] \overrightarrow{VT} [/tex] it is a vector
[tex] \overline{VT} [/tex] it is a segment
[tex]V, T[/tex] they are points
[tex] \overleftrightarrow{VT} [/tex] it is a line