A centripetal force is a force that makes a body follow a curved path. The direction of the centripetal force is always orthogonal to the motion of the body and towards the fixed point of the instantaneous centre of curvature of the path.
For a stone rotated in a circle by a string, the centripetal force is provided by the tension in the string. The centripetal force for motion of a planet around the sun is the gravitational force on the planet due to the sun. For a car taking a circular turn on a horizontal road, the centripetal force is the force of friction.
The centripetal force required for circular motion is along the surface of the road, and is provided
by the component of the contact force between road and the car tyres along the surface. This by definition is the frictional force.
