To play 720p HD video, an iTunes LP or iTunes Extras, a 2.0GHz Intel Core 2 Duo or faster processor 1GB of RAM and an Intel GMA X3000, ATI Radeon X1300 or NVIDIA GeForce 6150 or better are required.

To play standard-definition video from the iTunes Store, an Intel Pentium D or faster processor, 512MB of RAM and a DirectX 9.0–compatible video card are required.

PC with a 1GHz Intel or AMD processor with support for SSE2 and 512MB of RAM.

Once it is finished, you have successfully transferred purchased music from iPhone to iTunes. This will start the process of copying purchases to iTunes. Choose Devices listed under it, and then pick Transfer purchases from ‘iPhone’ (or whatever your device name is). Next thing you need to do is to turn your attention to the File section in the upper part of the screen.

Make sure that you have entered the same ID you are using on your iPhone. You will notice a dialog box where you will be asked to enter your Apple ID and password. You can do this by selecting Store from the top menu, and then choosing the option Authorize this Computer. If this is your first time using iTunes, you will need to authorize you Mac. After it finishes connecting it, you can see your iPhone in the list of devices. When you connect your device, iTunes will recognize it automatically. It is recommended to use an original USB cord, in order to avoid any issues during the process. Once you have installed iTunes on your device, launch it and connect your device with a USB cord. If you already have iTunes installed on your Mac, please make sure that you have most recent version of the software.

This can be done easily from the Apple website.

Install itunes on mac