Question

what is friction?
how friction is caused?

Answer 1

friction is opposite force exerted by any thing
it is caused when 2 things are in contact

Answer 2

Answer:

What is friction?

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Friction opposes the relative motion between two surfaces in contact . It acts on both the surfaces.

What causes friction?

Friction is cause due to the interlocking of irregularities between the two surfaces in contact.

Smooth surfaces have minute irregularities between the two surfaces. Rough surface have larger irregularities between the two surfaces. So force of friction is more if the surface are rough.

(You can refer the image attached with my answer )

Hope it helps you :)