MibbitIRC places a pre-created Mibbit chatroom into a page with a certain div on it. This can be on any page: however, you only have one chat that it automatically connects to.
Note that you must have a Mibbit IRC chatroom set up already. This can be done from mibbit.com, and WikiHow has a guide explaining how.
Insert this in a page to render the widget:
data-server="the name of your server"
data-channel="the name of your channel"
>This text will display while the widget is loading.</div>
This text will display while the widget is loading.