To add a new site to the quick launch bar in SharePoint click Site Actions > Site Settings and under Look and Feel, click Navigation.
Check Show subsites under Global Navigation and also under Current Navigation.
Once you have checked these, you can rearrange and hide items if you scroll to the bottom of the window. Sub sites that will now show on the top link bar are listed under Global Navigation. Sub sites that will now show on the quick launch are listed under Current Navigation.
You can select a link to move it up or down. Select a link and click Delete or Hide so that it will not show.