work is the measure of a quantity that is capable of accomplishing macroscopic motion of a system due to the action of a force over a distance.
W = F.S
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