If you are already part of the Department of Computer Science (or Electrical and Computer Engineering) at Duke University, reach out to me via email. I'm happy to schedule some time to chat with you.
Otherwise, submitting a formal application is a necessary first step. Please see Duke's Graduate School Application Instructions and Duke CS's Prospective Student Page for more details on how to apply. Please make sure to indicate me as a potential advisor on your application. You are welcome to send me an email to introduce yourself in parallel with the application process, but know that I may not respond until the department's decision-making timeframe.
If you are currently an undergraduate at Duke, reach out to me via email. Please include a description of your interests along with a list of relevant courses that you have taken. It is helpful, but not necessary, if you have taken a course with me in the past.