How to make a ring tone

See this article.

Create a ringtone of your Logic Pro or GarageBand for Mac song - Apple Support

You can download Garangeband to your iPhone, and use the app to make ringtones, and import them into the iOS ringtone menu. Garageband can be downloaded from the App Store for free.

So you don't need a Mac to do this, but can do it all directly on your iPhone. What you want to use as a ringtone is up to you - you can download ringtones in various places on the web, for example on Zedge. You save the ringtones in the Files app on your iPhone, then you are ready to import them into Garageband and turn them into ringtones.

I have made an easy guide that shows you how to do it step by step:

Create Ringtones in Garageband - Apple Community