YTMP3 works on Android because it runs in the browser: no app, no APK, nothing to install. Short version below; the full Android walkthrough lives on our sister site, which owns device guides for the network.
For the detailed guide, including download management, playback defaults, and troubleshooting Chrome warnings, read the full Android guide on OnlineVideoConverter, which owns device guides for the network.
Yes. Everything happens in Chrome; there is nothing to install and no app to grant permissions to.
Into the Downloads folder. Open the Files app or your file manager to play it.
App route: YTMP3 Android app.