A line segment with an arrow is vector.

End of line segment with arrow is head of vector and end without arrow is tail of vector. The length of vector is drawn according to magnitude of quantity.

E.g. : $4 \mathrm{~N}$ force is acting in East direction. Suppose, $1 \mathrm{~cm}$ is corresponding to $1 \mathrm{~N}$ force. Hence, $4 \mathrm{~cm}$ long vector can represent $4 \mathrm{~N}$ Force.