In order to accuse someone of slander, the victim must prove slanderous acts. Slanderous acts may be committed anonymously or directly. Those acts may include gossip which hurts the reputation of the victim.
Slanderous acts must have caused some damage to the reputation of a victim, including damage which may prevent job offers or other opportunities, in order for them to charge slander. The victim must be able to prove that the individual was directly responsible for either beginning the rumors or for spreading them, when those rumors harmed their reputation.
Slander is an act which is often handled in civil court. The case would likely include an attempt at monetary compensation for the slander. For example, the victim may sue for compensation because they were unable to find a job because of the slanderous act.