Work is defined as the energy required or energy produced to displace a particle for some distance by the action of a force.
Consider a particle is in rest ,a person(mainly a force 'F') is displaced it by a distance 'S'. Now we can say that this person done a work against the friction ,which is equal to -
Work-done by man = F.S
Also we can say that Work done by friction is equal to
W' = - F.S