Hi, im having problems to undestand the IUserPresence self variable

im using unity sdk btw, and im creating some friends match between two friends players.

 IUserPresence self = null;
        socket.ReceivedMatchPresence += presenceEvent =>
            foreach (var presence in presenceEvent.Leaves)
            // Remove yourself from connected opponents.
            Debug.LogFormat("Connected opponents: [{0}]", string.Join(",\n  ", connectedOpponents));

i have taken this from the docs but the IUserPresence self = null; declaration i had to made it myself due it was giving me errors due not reconizing the self variable, and im wondering if declaring the variable as i did up there its the right way? due im not have idea where to get this can some one guide me ? please? thanks