For an object to move, the forces on it must be unbalanced.
In the diagram below, the duck is floating on the water. It is not moving up or down because the force acting downwards (caused by gravity) is equal to the force of the water pushing up on to the duck (upthrust).
The force of gravity (red arrow) is equal to the upthrust (green arrow) from the water.
The car shown below is accelerating because the driving force (green arrow) is greater than the drag caused by air resistance (red arrow).
The car is accelerating left to right because the driving force is greater than the air resistance
When the drag is greater than the driving force, the car will slow down; but if they are balanced and the car is already moving, it will continue to move at a constant speed. This is described in more detail in Isaac Newton's 'Laws of Motion'.
There are many forces acting on a skydiver when they leave the plane:
As a skydiver leaves the plane, they accelerate downwards due to gravity, but as their speed increases, so does the air resistance. This continues until both forces are balanced and the skydiver will fall at a constant speed, called their terminal velocity.