Welcome to the world of apple!
Are you talking about downloading music that you have previously purchased from iTunes? If so, you and your husband will both need your phones to be registered to the same apple ID (essentially an email address) to be able to access the same purchase history.
If he is trying to download music that he has purchased from his own account I'm not sure why he isn't able to. The easiest way to see your purchased music is to open the iTunes app, click "more" in the bottom right hand corner and then click purchased. Here you can see all songs that you have purchased with that account and should be able to easily re-download them.
If this doesn't help, you can get help directly by filling in this easy-to-use form. https://expresslane.apple.com/GetproductgroupList.action
Feel free to reply with any more questions about your issue or contacting apple.