^^^ Oh my goodness.
Although FlyingRon has provided you with excellent information on the DMCA takedown notices that allow you to have infringed content removed from sites hosting your copyrighted material without your permission, equally important can be to protect your works from being infringed in the first place.
There are several ways you can make your copyrighted works less vulnerable to infringement. One way is to use the copyright symbol (©) along with the date of your creation and signature on all of your works. Although the © is no longer necessary - copyrights are automatic once the work is fixed in a tangible form - the symbol provides notice to others that your works are rights-protected.
If you have your own website, providing a copyright notice on the site can also help, stating that everything on the site is rights-protected. You can provide along with this notice your contact information and licensing information. Those who wish to use your works can contact you for a license.
It is up to each copyright holder to police the internet for infringement of their works and this can be quite the task. There are tools available for monitoring the internet, however, that make this easier (check out resources like "Google Alerts").
If you find that your works are infringed, you can then follow the steps outlined by FlyingRon to have your works removed from their online locations. If removal alone is not enough to remedy the harm caused by the unauthorized use of your works, you can consider sending a demand letter requesting compensation and/or you can sue the infringer.
Although federal registration of your copyrights is not necessary, registration of your works prior to infringement makes you eligible to collect statutory damages. Statutory damages range from $750 to $30,000 per infringed work, or up to $150,000 per infringed work for especially egregious, willful infringement. The cost to register a work is small ($35) and the benefits can be large.
Good luck.