A simple bearing, like the kind found in a skate wheel. Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers "bear" the load, allowing the device to spin smoothly.
Ball bearings are used in between two objects to move an object over the other smoothly.
These are used to create less friction between any flat surfaces.
The roundness of ball bearings would help them to roll along with the objects.
As we know that Rolling friction is always less than the sliding friction.
The sliding friction between the axle and the wheel is converted in to rolling friction by placing ball bearings between the axle and the wheel.
Ball bearings support rotatory parts to facilitate smooth operation and reduce friction.