It's a little unclear to me from your post whether you are looking for info on registering copyrights on your content, or registering a designated DMCA compliance agent for your site, so there are links for info on both below.
If you're looking to register copyrights on content that you've shot,
check out the information here.
If you need to register a designated compliance agent for your site (whether that agent is to be you, or someone else), then
the info you need can be found here.
Hope this helps.