?? You’ve never installed a U3 app before?? Goodness!! 
On the U3 Launchpad menu window click on Add Programs >> then click on Install from My Computer. In the Open window find the .u3p file you downloaded and click the Open button, this will open the U3 Add Program Wizard, click Next and etc to install the PAMenu app.
That gives you the connection between U3’s Launchpad and your PortableApp.com menu and it’s apps and suite that you installed to the data/file portion of the U3 stick. (You have installed Portableapps already haven’t you? http://portableapps.com/suite )
hth
