In IRC, commands start with a forward slash, so if you want to use a forward slash as the first character of a line, you have to escape the forward slash. This is done by using two forward slashes. For example, if you wanted to say "/cs aop #chan add nick is the command to add somebody to the auto-op list", you would type in the input line the following:
//cs aop #chan add nick is the command to add somebody to the auto-op list
In the Twitter tab, you may not send messages starting with a forward slash without escaping it. If you do not escape the forward slash, you get the following message:
<Twitter>: Message not sent. Use // if you really mean it.