$\left\{\begin{array}{l}\overrightarrow{u}=\overrightarrow{PQ}\\ \overrightarrow{v}=\overrightarrow{PS}\end{array}\right.$

with the arrow over the top showing the direction.

This may seem slightly counter-intuitive at first. But if we add in some possible figures you can see how it works. If $\overrightarrow{u}$ moves 5 units to the left and $\overrightarrow{v}$ moves 1 unit to the right (−left) and 3 units down.

Then $\overrightarrow{PR}=\overrightarrow{u}+\overrightarrow{v}=5$ units to the left −1 unit to the right and 3 units down = 4 units to the left and 3 units down.