Converting mp3 files in iTunes

I have been trying so hard to convert a couple of mp3 songs to ringtones on my iPhone 7 and OMG it is SO FRUSTRATING! I know I am an average user of iTunes but honestly it should not be that complicated to convert a file, other operating systems you simply paste the file and that's it. iTunes is definitely not user friendly here.

I read some threads on google on how to do this and they all seem to be giving direction on how it can be done using the older versions of iTunes, definitely not the latest.

Would be great if someone could shed a light on how this can be done under the latest iTunes version.