There is no such thing as Copyright Free music! All intellectual property (IP) including music, written work, art, ideas, etc., are protected the second they are created under U.S. Copyright law (and similarly, copyright laws and international treaties around the world), whether it is registered or not. While registering the work offers additional bonuses and protections, it is not necessary to claim a copyright.
In order to use someone else's intellectual property, you need the creators permission or a 'license'. Such a license can be publicly or privately granted. Examples of both are below.
Public Licenses granted by a content creator or IP rights holder could include creative commons licenses or proprietary programs such as FiXT's YouTube Music Program. Public licenses are usually conditional, meaning that for you to use the material legally you have to perform a certain action or give proper credit when you do so or are limited to the type of content you can use it in. Some public licenses have no conditions or restrictions. It is very important that you find an official source that states whether a work is granted under a public license and that you follow the conditions put forth for the use. Otherwise, you are in violation of your license and subject to whatever penalties may apply.
For example, to use a song cleared by FiXT's YouTube Music Program, it may not be a 'professional production' such as a feature film, you may not advertise a product in the video, you may not enable ads or monetize the video in any way, and you have to provide a proper credit to the artist and a store link in the format provided on the Podsafe Page. In return, you are granted the publicly announced permission to post that song in your digital content without having to obtain a written statement, and you can simply refer anyone who questions the use back to the Podsafe page that states the terms of the public use.
Private Licenses are usually obtained direct from a content creator or IP rights holder and may still be extremely conditional. Private licenses may involve some kind of exchange of services (for example - an artist may allow someone to use his music in return for a service the user can provide, such as helping manage a social media page or doing some promotion in return) or a monetary exchange. There are still conditions you have to follow which can include where you can use the copyright material or whether or not you have to provide credit, even after paying for the use, or you can be in violation of the license and subject to penalties.
The FiXT YouTube Music Program is an example of a private license granted by an IP rights holder. In this case, you would exchange a predetermined amount of money for the 'license' or 'rights' to use music in a video you plan to make money off of or monetize with ads, but there are still conditions you have to follow.
For additional basic copyright information, there are a number of great resources on the Web. YouTube has a wonderful help & FAQ section on copyrights, and this site also does a pretty good job giving a basic explanation of how copyright works.
We encourage all content creators to get educated on the basics of copyright as it can affect you in all sorts of ways!