My teacher told me that this was because frictional force resists relative motion between the engine and the car. However, in this case it seems to allow relative motion between the ground and the car.
Answer
[...] it seems to allow relative motion between the ground and the car.
While there is relative motion between car and ground, there is not relative motion between wheel and ground. And that's what matters, because that's where the friction is.
Think of walking. Your body moves relative to the ground. But at each step, your foot on the ground is stationary. Your foot pushes on the ground backwards. Static friction holds back forwards to avoid that your foot slides.
On a car's wheel, the same happens, just at each new point that continuously comes in contact with the ground. For that short moment that it is in contact, that point is stationary and there is no sliding. That point pushes backwards, and so a static friction pushes forwards to avoid sliding (to avoid wheel spin).
Also, is friction a reaction force?
You can think of static friction as a reaction force, if you will. It only exists because your leg - or the car's wheel - applies a force backwards on the ground.
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