I usually log on when I turn up to IW and check it every so often to see if anyone joins me but it hasn't been very busy lately

I drop by on occasion. Usually no one there.

lonesome in there...........

There's the /me, /topic and /nick Talthy mentioned, but besides that one and some mod commands used for kicking, banning and things like that I'll not mention, that leaves only the /msg command.

if you type <font color=red>/msg guest Hello there!</font>, a window will pop up on Guest's computer with your message and a bar fo typing replies. Once Guest replies, you get another small window with bar as well and you can talk privately.
Instead uf using /msg, you can also double-click on the person's name in the list to the right, which has much the same effects except that you both get a window right away.

There's also the quit command, but since you can't really change channels either that's practically pointless. If you type <font color=Red>/quit the milk is cooking</font> you disconnect from the chat and people would see that it was because the milk was cooking.

Other commands you can normally use with IRC don't work in the browser version, so no underlining, no partially coloured messages, no aliasses (sort of like personal shortcuts to long lines, URLs, things like that) and so on. So your list would be:

/me message
/msg name message
/nick newname
/quit reason
/topic message