If you're finding it hard getting to grips with iTunes you should try the Help Menu at the top of the iTunes windows.
Click on the subject area you want to learn and need help with.
This usually helps most users sort out their problems.
If that fails, use the Apple Web Site Support Section.
http://www.apple.com/uk/support/itunes/
The web site will also help you with the iPod Nano.
If you think you need a book / manual - try this book:
http://www.amazon.co.uk/iPod-Missing-Manual-Ju de-Biersdorfer/dp/0596514913/ref=sr_1_1?ie=UTF 8&s=books&qid=1207175153&sr=8-1
Also, don't get iTunes and the iTunes Music Store confused,
they are both different - iTunes to play and organise your music and iTunes Music Store to purchase your music.
You don't have to use the iTunes Music Store to buy your music, as iTunes and your iPod will play MP3 files.