Two or more velocities add by

Two or more velocities add by vector sum.

In fact, velocity is a vector, with its own intensity, direction and verse. Therefore, we cannot simply add two velocities by algebraic sum, but we need to decompose them on two axes (if we are in a 2D-plane) and calculate the resultant on each axis, and then calculate the total resultant of the two vectors, which will have its intensity, direction and verse.