I want to download songs for free in my iPhone iOS 7.0

In what manner? If you mean Apple Music (which is not free):

Typical of Apple who assumes everybody runs only the latest software so there is no need to post system requirements, I had to go off-site to find this: http://www.imore.com/apple-music-faq - "Apple Music is available on the iPhone, iPad, and iPod touch running iOS 8.4 or later;