"+censor user" will place 'user' on your censor list. When a player is on your censor list, you will not hear anything from them when they tell, shout or say. Use "-censor user" to remove someone from your censor list, "=censor" to view the list.
When someone is on your censor list and sends you a direct message using "tell", he/she will be notified of his/her being on your censor list.