Friction is the opposing force that comes into play when one body moves or tries to move over another body. Friction depends on the nature of the surfaces in contact, how hard the two surfaces press together. For a given pair of surfaces, friction depends upon the state of smoothness of those surfaces.
The three types of friction are static, sliding and rolling frictions. Static friction is the friction which acts on an object when we try to move an object from rest. Sliding friction is the friction which acts on an object when it is sliding over another object. Rolling friction is the friction which comes into play when one body rolls over another body. Friction is both a necessity and an evil for us. It has both advantages and disadvantages.
To increase the force of friction, we need to increase the roughness of the two surfaces in contact.
To reduce the frictional force, we need to reduce the roughness of the two surfaces in contact by using lubricants.
Fluid friction is the frictional force exerted by fluids i.e., liquids and gases. Fluid friction can be reduced by giving suitable shapes to the bodies moving in fluids.