1) Creating the arena using:

/murder create <arena name> [min players] [max players]
where min players is equal to the minimun amount of players 
to make the arena start, and max players to the maximum 
amount of players that an arena can have.


2) Editing the arena using:

/murder edit <arena name>
in this menu you can add spawn points and set up the sign to
enter the arena: the spawn points are where the players will
spawn when they enter the arena, while the sign is just the 
way to enter it (by clicking it).


3) Setting the match duration in the editor menu by 
clicking on the clock in the settings.


4) Enabling the arena in the editor or using:

/murder enable <arena name>


Once you've done this you can click the sign and start 
playing :)
Use /help murder to see all the commands.