It is so easy to use U3P files on your Portable apps usb.
I figured it out myself and I am only 16.
First open your .U3P file with (Rar) - There you will noramly see 3 or 4 folders
Extract them with rar and you will now have a folder made with the uncompressed folders, in that 1 folder.
Now open the folders one by one and look for the exe file of the app and move it outside the folder so you have Appfolder---Folder,Folder,App.exe. and put this Appfolder in (portable apps) in your usb.
Then Refresh your apps icons in Options then the app should appear in the list.
Some apps may need you to move all the contents in that folder which contains the exe file. Do not do this with all apps because you may then have unwanted stuff in your list.
Hope this helps