How to set a ringtone on iPhone?

Hi everybody
I am having trouble with how to install ringtones on iPhone, this is really different from my previous Android phone. Can someone who does this guide give me more details or share an address so I can install it?
Thank you very much.
Thank you for reading my post, I have found how to set a ringtone for my phone. Here is the address where I download the phone ringtone and how to install the ringtone: “Zil Sesi” , “