This first example we have seen already in 14.2.4 Some Important Conjunctions - aber. If we now check whether the position of the verb changes we'll notice that this is not the case.

aber = but

Er glaubt es. He believes so.   Er weiß es nicht. He doesn't know.   Er glaubt es, aber er weiß es nicht. He believes so, but doesn't know.     Er kauft sich ein Auto. He buys a car.   Er hat keinen Führerschein. He doesn't have a drivers licence.     Er kauft sich ein Auto, aber er hat keinen Führerschein. He buys a car but he doesn't have a drivers licence.

And then there are some other conjunctions that do not cause a change of the position of the verb, e.g. denn.

denn = because

Er kauft sich kein Auto. He doesn't buy a car.   Er hat kein Geld. He has no money.   Er kauft sich kein Auto, denn er hat kein Geld. He doesn't buy a car because he has no money.