"Activating Street Pass You must register at the HH Showcase (page 11) located on Main Street to begin using StreetPass. "
... (page 11)
"Happy Home Showcase In the Happy Home Showcase (HH Showcase), you can view the model homes of other players after you have recieved them through SpotPass (page 13) or StreetPass (page 14). You can also place orders for many of the furniture and other items can see in model homes. And you can configure your StreetPass settings here. Note: You can keep up to 48 model homes at one time."