i download stuff from itunes on my pc while the ipad is connected to it by cable and i enabled all options about sharing between them but.... only books and newsstand appear on the ipad after i download them while apps and itunesU appear on pc ONLY ,,,,,, Any help !
For some reason iTune U courses only seem to work properly if you subscribe to them in the iTunes U app on the iPad. Collections usually sync well enough. I've taken to subscribing to collection on the computer (because it manages this kind of subscription better) and courses only on the iPad in iTunes U. If I need some specific bit of media on the computer, I download just that item from the course.
Tedious, but it works.
As well as turning App syncing on, you also need to make sure that every app you want on the iPad has a checkmark next to it. This doesn't always happen when you purchase a new app from the computer; possibly because there is not way to determine what device (if you have more than one) you wanted the app on.
Again, to simplify things, I try to download all my apps directly to the iPad. As long as you have things set up properly in the App sync section, they will be copied to the computer on the next sync. If they are not, you can always right click on your iPad in iTunes and choose Transfer Purchases. This will copy most iTunes media purchased on the iPad to the computer's iTunes library.