How to write a vector in Latex

To write a vector in Latex, we can use \vec function

$\vec{AB} = 0_E$
\[\vec{AB} = 0_E\]

or\overrightarrow function

$\overrightarrow{AB} = 0_E$
\[\overrightarrow{AB} = 0_E\]

Note: as {Keyboard warrior} said in the comments \overrightarrow function looks more like the vector symbol(s) we see in textbooks.