Most of it is pretty obvious, the only two lines that need explanation are the last one of XMPP and the last one of IRC.
The variable "owner" is a string that will be printed when issuing the ".help" command. It can be just something like "drymer on XMPP muc" or just a name, your choice.
Respect the variable "line", when joining a muc you receive the last 20 messages send, which would be relayed to the IRC channel. With this variable, the bot will ignore the default 20 lines. Change it if the XMPP server has non-standard messages retrieve.