After authenticating who you are via Twitter, you will be allowed to start adding your items one by one until you have built your whole collection up. And the collection itself can be marked as either public or private. That depends on the actual nature of what you collect, and how much of a showoff you really are.
If you want everybody to know you have that mega-rare baseball card in your possession, then go ahead and label the whole collection as public. You might not be willing to lend it to anybody, and that is just fine. In addition to letting you track who has your stuff, this site aims to let you get self-organized. Both uses are entirely legit.
HereIsMyStuff.com In Their Own Words
Your personal inventory manager.
Why HereIsMyStuff.com It Might Be A Killer
It turns bookkeeping into a thing of the past.