IPad – How to play an mp3 on the iPad

I'm not trained on iOS and my iPad 6th Gen is the only Apple product I own.

iOS version is 13.3.
I have downloaded the app called, "Music"
I have downloaded Readdle Documents.

Using Documents, I have downloaded an mp3 file. Now I'm not sure how to get the Music app to "see" it.
It seems like I need to add it to "Music's" Library, but cannot find the option to do so.

One solution I recall but can’t cite said to install an app called "iTunes", but I could not find it in the app store. I did find "iTunes Store" but that seems to only be a way to purchase content.

• I am looking to use the content I already own.
• I have no access to a desktop system that I can install software on, so any external or 3rd party tools are not accessible.
• I don’t know how I’ll bulk load mp3 as well since I lack a computer and readdle won’t let me manage playlists.

Can someone get me started to how to play MP3?