To upload, you need an account and a guild. Start the client and click the third button from the left. Go back into WoW and type /combatlog. Kill something, click the "Open Report" button to view the report in a new window.
If you're just visiting, find your realm on the realms page, go to your guild and click on any report to view it. Or just get back to the front page and click on any fight to find kills for that boss.