If you have no idea what Dragon Age Keep is, BioWare gave a brief summary:
It’s a companion Web experience that allows you to customize your story choices across the Dragon Age franchise. This ensures that regardless of what platform you play on, you’ll always have your Thedas the way you made it.
For some time now, Dragon Age Keep has been going through a closed beta. If you’d like to participate, apply online over here, with people chosen “based on their application responses, not on a first-come first-serve basis. This way, we can make sure that we have users from multiple platforms and with varying levels of experience with Dragon Age games.”
To get all the information about Dragon Age Keep, BioWare put up a FAQ on their forums, which reveals that you need an Origin ID to log in, Keep isn’t mandatory, and more.