A single object usually has multiple forces pulling on it at once. Gravity pulls it down, the floor pushes it up, engines drive it forward, and friction drags it back. The single force that has the exact same effect as all these combined is called the resultant force.
If forces are balanced, the resultant force is zero, and the object stays at rest or continues at a steady speed in a straight line. If forces are unbalanced, the resultant force is not zero, and the object accelerates or decelerates.
In a straight line, you simply add forces in the same direction and subtract forces acting in the opposite direction. Push the driving force higher than the resistive force and watch the car accelerate. Balance them out again, and the car does not stop; it simply locks into a steady speed.
The greatest trap in physics is believing an object needs a forward resultant force to keep moving. It does not. A car cruising at a steady 30 m/s on a highway has a resultant force of absolutely zero because the engine's push perfectly balances the air resistance. A forward resultant force is only needed to accelerate and change the speed.
A cyclist and her bicycle have a total mass of 80 kg. She pedals with a forward force of 150 N against a total drag of 30 N. Calculate the resultant force and her acceleration.