Newton's First Law of Motion states that an object at rest or uniform motion tends to stay in that state of motion unless an unbalanced, external force acts on it. Say if I were in a car and I push it from the inside. It won't move. So how is the engine of a car capable of moving the car?
The car's engine tries to make the wheels turn. However, the wheels encounter friction against the road so they cannot just spin. As the road has much higher inertia than the car, it will not move when the wheels want to turn. Instead, it is the car that moves.
The end effect is that the engine pushes against the road, just as you do when you push the car: your feet are on the road, allowing you to push the car forward. In the case of the car, the wheels are on the road and they can push the car.
Pushing the car assumes you have enough force, and the road is not too slippery. This also applies to the engine: if it does not have enough power, or the road is too slippery (icy), it cannot push the car.
Each force causes reaction (3rd law). If move a car from the inside the car moves you as well. That's because you are pushing or pulling. However the engine does not push but converts energy in other directions, usually a rotating one (the same as riding a bicycle). This rotating force has its counter-force which is reaction of ground.
Pushing a car you use a friction force. Pushing from the inside this force is caused bythe object itself, not solid ground.
The friction force between the tyres and the ground makes the car change positions or move,if the road is slipperly cars find it difficult to move sometimes they can be just spinning on the same spot but again the energy supplied by the engine makes the crankshaft to rotate in the process making the tyres to rotate too hence that same energy together with the friction facilitates the car movement.
If you pushed very hard on the dashboard and let your effort throw you into the back seat, you might be able to move the car a little. When you landed the car might move back the other way. Internal forces within a system can move parts of it. Newtons first law applies to the center of mass of a system.
"External force" on a system can be a reaction force to the system exerting force on something else. For example, if you opened the car door and used your foot to push the car forward you might be able to move the car. The force your foot is exerting on the ground is not an external force upon the system of you and the car. But the equal and opposite frictional force from the ground on your hand or foot is an external force to the system.