When one party has made initial contact, whether by phone or by e-mail, the mediator will usually expect to speak with the second party to invite him/her to come to mediation.
Assuming that both parties are willing to try mediation the Mediator will arrange to see the clients, initially seeing each party on a one to one basis and only seeing the parties together once they have each been seen alone, and only if the parties wish.
The Mediator will make it clear to the parties what they need to bring, and will usually confirm this all by email