Where two conflicting parties cannot reach agreement on the issue causing the conflict, they can agree to ask a third party (a mediator) to help them reach a solution. A mediator is a person who acts as a facilitator between the parties but does not make a decision about who is right or wrong. So, a mediator is not a judge.
The mediator goes on assisting both sides until the parties themselves come to an agreement. If it is clear that the parties are not going to reach an agreement, the mediator might have to withdraw from the process. The parties will then have to find another way to resolve their conflict, for example, by using arbitration or going to court. (See: Settling Disputes Outside of Court)
The main job of a mediator is to keep the parties in the negotiation communicating with each other. To do this the mediator must get the trust and confidence of both parties and keep this trust by always being objective. The mediator must try to find out exactly what the problem or conflict is about. When the two sides meet together the mediator must encourage both sides to be realistic about what they want from the other side and what they are prepared to give.
If you are representing a person or group at a mediation you need to prepare for the mediation in the same way as for a negotiation.