As posted above it depends on which MacBook you have, the old white or black MacBooks use MiniDVI (that one odd port you don't know what is for) for external displays.
He posted a link for the Mini DVI to DVI connection which is useable on TV's that have DVI (since you mentioned HDMI, as some higher end TV's or HD displays will have that) however there is one thing to note with that. You can't use a dual-link (I think there are various names for it) DVI cable with that, you can only use a single-link. Basically, there is one horizontal pin on DVI connections, dual link has 4 extra pins, 2 above that horizontal one, and 2 below it. So keep that in mind if you go that route as the graphics card isn't that powerful in the MacBooks.
Also, as the sound and video cards are separate, even if you ended up with some way to get to HDMI, you would still have to do sound with a different cable coming from the headphone jack on your machine as he mentioned.