ok first you need type /list
this will give the list of players that are on and what area they are in

Second once you find out what area they in for example we say they in the Forest.
you would type /Forest message.
now make sure first letter of the area is capital and second make sure there is a space between the area and your message

now it will show up on your screen , but no one else in the area you are in will see it. Every one in the area you sent the message to will.