HOW DO I GET MY MUSIC FROM MY IPHONE TO MY COMPUTER?

I had all my song on my laptop which died. Everything was lost together with my itunes. Now it says which I can usually sync my iphone to one mechanism and wants to erase everything. How do I get all my song behind on my computer? What about my apps? How do I supplement song that’s on my mechanism right away on my iphone when it keeps observant which i have to erase everything?