What is a resultant vectors direction?

It depends. I do not know if you are adding vectors in 1D, 2D or even 3D.

In 1D: its direction is along the x axis if its positive, otherwise it is in the opposite direction

In 2D: its direction is along the x or y axis if its component is positive, otherwise it is in the opposite direction

In 3D: its direction is along the x, y or z axis if its component is positive, otherwise it is in the opposite direction

That completely depends on all sizes and all directions of all of the vectors that combined to produce the resultant one.