How to put my own ringtone onto an iphone 4s?

I have an iphone 4s and want to put a particular song as my ringtone. I have attempted to follow some instructions but they seem to miss out essential steps! I then tried the downloads but many then said I had to sign up etc. I only want 1 song, surely Apple know this kind of stuff really puts people off buying another iphone?

You probably would just have to go into the iTunes store app, and just download a ringtone for approx. 1.29$. Unless you can find an app, a website that will allow you to send the song, or to jailbreak your phone.