How to create a responsive theme with Omega?
So, there's plenty of good documentation on both Omega 3 and Omega 4. Depending on what your background is and what your experience level is there are a number of ways to approach responsive design. I suggest defining your needs for a responsive website, and then seeing how Omega can help you. If not Omega, than the Zen and Adaptive themes are also well documented. There are free tutorials and videos on youtube, your question here is too generic to answer.