Speed and Direction determines an objects' velocity. And that's why the formula for velocity is similar to speed.
The formula is that you have to divide the distance by the time it takes you to travel that same exact distance, then you have to add your direction.
But if you're talking about what determines an objects Terminal velocity, then, gravity and drag determines it because gravity speeds the object up while drag (which is caused by friction) slows it down. And when these two forces are applied to an object, the certain object is said ti have reached it Terminal velocity.
If you still need help feel free to message me :)