The similarities between the vertical and horizontal scroll bar are:
They enable one to scroll in alternate directions. For the vertical scroll bar, the direction is up-down and vice versa. While the horizontal bar enables extended view of the screen or document from right to left and vice versa.
They are usually found on the edge of the screen
In come programmes or apps, they can be hidden one docked so that they are visual accessible always.
They are independent of one another. That is, while doing a vertical scroll, it does not actuate scrolling on the horizontal scroll. The obverse is also true.