When you put code on GitHub, you retain all the copyright to your code.
However, you do grant GitHub a license to host the code, and you also allow GitHub users a set of rights - namely the ability to look at, and fork your repository. These are terms that you have accepted when accepting their Terms of Service when creating a GitHub account.
Even when you upload code to someone else's repository (such as via pull request), you still own the copyright to that code, unless you have signed a copyright assignment agreement. You own the code, but you may be providing the code when uploading the code to the repository. For example, if you upload code to an Apache licensed repository, you submit your contributions under the Apache license as well. This gives others rights to your code, but you still retain the copyright.
Would adding a license stating that I own the code and the terms of usage suffice in this situation?
A license is used to grant rights to other people. If you want to explicitly assert copyright to your code (which is recommended, but not necessary as all copyright is automatic), then you can use the following header:
Copyright © 2016 Riptyde4