How do i use down load music for my ringtone - Apple Iphone 4s I Phone 4 S Factory Unlocked Sim Free 16gb - White

It's a bit complicated to add ringtone to iPhone, because the format for iPhone ringtone is m4r, which need to be made specially. You can use iTunes to make ringtone on computer or GarageBand to make ringtone on iPhone. Here I found a tutorial for your reference: https://all-things-about-apple.blogspot.com/2021/05/how-to-change-iphone-ringtone.html

You can firstly download music on your iPhone then set it as the ringtone. I recently found a great app to download music for free. You don't need to pay for each song downloaded, you just need to enter the song or singer you want then press search button, click the one you needed to download. Free try here if needed:
Any MP3 Downloader Music Downloader for Mac

It is a long process. if you are up to it this is a pretty good guide
http://technologyguy.hubpages.com/hub/Convert-iTunes-music-into-ringtone-for-iPhone

it is most definitely easier to get one of the free ringtone maker app for you phone. just know that most are going to limit you to 30 - 45 seconds of the song. good thing about it is that you can choose which portion of the song you want