Q: Itunes on my ipad is showing three options itunes U , podcast , and download. I want to download music how should i do that?

You can only purchase content that Apple is allowed to sell in your country. You can check what is available where you live here.

http://support.apple.com/kb/ts3599

What country are you in ? Not all content types are available in all countries (what is available where is shown on this page). If you are not in a country where you can buy music from Apple, then are there other music purchase download sites that you can use ? You can also copy your own CDs via your computer's iTunes.