Examples what I use them for is the Google custom search at the top of the main column and the AdSense link units below this blog title. A blogger also wanted to add a Marquee like the one above the blog title in the demo blog. This can be done by adding extra ADD A GADGET. To do this, go to LAYOUT, click EDIT HTML. This will take you to the template editor.
Look for showaddelement . Change showaddelement='no' to showaddelement='yes' If there is a a maxwidgets='1' in front of the showaddelement. Change it to maxwidgets='2' or more or even leave it as maxwidgets='' (unlimited number). If you have problem looking for the above, press ctrl+F and search.
The above (searchbox, ad unit, marquee) were added using a
HTML/Javascript gadget. Whatever you add can be dragged to any sections
of your blog using your mouse.