dear student
centrepetal force is not a fundamental force . any force which always act perpendicular to the direction of velocity of particle can be said as centrepetal force .
no its is not constant vector . its direction keeps on changing weather motion is uniform or non uniform
if a car is taking turn on unbanked road only friction between tyres and road is providing centrepetal force
if car is going on a road which is banking on some angle with the horizontal component of normal force along center or if needed friction will provide necessory centrepetal force