There's a decent YouTube app' also, think you probably had that pre installed though? If not, get the YouTube app!! There are a load of Sony apps specifically for the Xperia range, easiest way to find them, or any other app', is on your PC. Log in to the Google Play Store and just search "Sony". if you find anything you want just hit the "Install" button - you probably knew that anyway though!!
If you want to customise your phone and change the icons you'll need Go Laincher and Go Locker. Go Launcher changes the whole set up, wallpapers, themes, screen transitions etc, Go Locker sets the "lock screen", adds new icons for any home screen on your phone and changes the icons of any apps on the phone. If you want to try those I'll be happy to help out.
If you're not on Jellybean 4.2 ... plug your phone into your PC with the supplied usb cable and any updates will be downloaded and applied. You'll be prompted to back up the phone first but that's easy enough. It will also install "Sony PC Companion" on your PC, That will let you scnc your phone's data with the PC, also helps transfer music and images to and from phone and PC.
Finally!! There are very good Xperia forums online, so if you do get stuck feel free to ask me or check out the forums here: