Fans don't ever "run by themselves". Like like asking if you have to put gas in your car or if it just "runs by itself". LOL.
Yes, they must be connected to either a fan hub, that in turn must be connected to one of the motherboard fan headers, OR, they must be connected to the motherboard themselves. Not a problem having only two fan headers so long as they are of the same type as your fans, 4 pin PWM or 3 pin DC controlled, whichever yours comes with, OR if your motherboard has the ability to choose whether they are going to be PWM or DC controlled which MOST modern motherboards can do. That is a very low end model though, at the bottom of the B450 product stack, so I don't know if that unit's BIOS has that ability or not. You'll...