Copyrights

This is a right that automatically accrues to authors when they create games, music, text, etc. This right allows the author to say, "Please don't use my work without my permission." Without this right, even if creator sell their anime, music, manga, or novel, the people who buy them will copy and distribute it as they please, and the creator will not be able to get money to living. If the creator can't get money to living, then there will be no one to make anime, music, manga, or novels, and the manga you are promoting will not be continued. That's why copyright exists.

Why you say it at here?

In other words, you can't use someone else's music without their permission. This is explicitly forbidden by law. Use only free materials that you own the rights to or can use within the terms of use.

But I use it only for private uses

If you publish it on the Internet, it is not for private use.

But I use it only for non-profit uses

It is forbidden to use other people's stuff without permission, regardless of whether it is for commercial or non-commercial use.

Original author saids it is free to use