The way things are set up nowadays, you don't need to do anything to have the copyright on your work, you own the copyright automatically just by producing it. It all comes down to proving that it's your own work. Therefore, whatever I might do, I've got the copyright to all my work on this site. In order to make my work available to people, I need to waive my rights.
There are various ways that I can waive particular rights while retaining others. The old-fashioned way is to grant permission to people who request it to make copies of my work. I can also write a statement giving permission for anyone to use my work in certain ways. This method is little more than an assurance that I will choose not to use my right to sue you for using my work if you use it in the specified way. If tested in court, my written statement would probably be enough to win you the case.
A more structured way that is being used now is to create a "Copyleft" licence, which is a formalised statement of the above scenario: an assertion of copyright combined with a written waiver of the right in defined circumstances. An organisation called Creative Commons has been started in the USA to help creators to open up their work to as much public use as possbile, while protecting them from being entirely ripped off by entrepeneurs.
You are free to use any of my work from this website for any non-profit making purpose. If you want to use it to make some money on, ask me. I might let you.