how to sync itunes music on my computer to my iphone5

Assuming you are talking about past purchases from iTunes use Apple article HT2519 and

HT 1689 has a lot of great FAQ's reguarding iTunes and how-to's that may help.

If the issue is something other that iTunes related, more information will be needed...

Hope this helps 🙂

thanks for quick response ..... hope I can find this information