Klines prohibit users from logging on to the server. This is used normally to restrict access from those that have been disruptive. To unkline someone you must either do it through the control panel or use the /unkline command. You can use wildcards while creating a ban, though you want to be careful not to make the kline more prohibitive than needed. The second example is a site ban and will prohibit anyone from that domain from using the server. Care should always be used when placing klines. Klines work the same way as room bans, except that they ban people from the server instead of from a room.
Examples:
/kline lamer@pm02.digex.net Flooding isn't allowed
/kline *@*.digex.net Flooding isn't allowed 30
A kline is often a good action to take against someone who refuses to behave despite having been killed a few times. They can still get onto the chat network if there is another server for them to use.