Its that square or rectangular thing situated next to your house. Usually accompanied with a big door. Maybe a few windows? If its anything like mine its filled with stuff that shoulda been thrown out years ago.
Or its a section to post pics of your car. Which i still havent figured out how to use!
In the "Quick Links" menu near the top of the page (next to "Search") click on "User Control Panel" then click on "Edit Your Garage" over to the left. Or just click here. You can fill out the form there as to make/model of your car, write some text about it, and upload pictures too.