Friction occurs because the surfaces of all objects, no matter how smooth they look, have tiny bumps and irregularities on them.
When two surfaces come into contact, these irregularities interlock or get stuck with each other.
This interlocking opposes motion and creates friction.

• Rough surfaces have more irregularities → more friction

• Smooth surfaces have fewer irregularities → less friction

So, friction depends mainly on the nature of the surfaces touching each other.