The HBC is a .dol loading application. In other words, if you haven't put any Wii applications on your SD card, nothing will show up!
Try downloading the Homebrew Browser (find it on the wiki) and putting that on the SD card (just put the contents of the "apps" folder in the download into the "apps" folder on your SD card). Then the HBB will show up in the HBC (sorry); launch it and you will be able to download all manner of wonderful things through a simple interface, which will then show up in the HBC. You can download the homebrew apps manually via PC from the wiki or elsewhere too, of course.