Copyright ownership does not mean something cannot be distributed or given away or copied, how would anyone publish anything then? Copyright ownership is merely legal control over how something is copied and distributed and the owner get's to define how people can and cannot copy their work. For example, the copyright owner of a book would allows a printer to create copies of their copyrighted content in each book that they print. There's limits on the control with things like fair use and the first sale doctrine.
A licence is merely a legal statement defining exactly how a given piece of copyrighted work can be copied. As the copyright owner, and only as the owner ultimately, you can licence the work in any way you want. The license may be fairly complex such is the case with the GPL however it does not need to be such as with the MIT license. A work with no copyright owner is in the public domain and can be distributed and copied and modified with no limits.
Licences differ from public domain in that the copyright owner can use the legal system to claim copyright infringement on those who break the licence. A work in the public domain has no copyright owner and as a result no one can take you to court over it or enforce any licence on the work (in theory, in practice money trumps everything).