I did this whole rigamarole in May, and found this link to be VERY helpful:
It walks you through what you’re trying to do, what you need, and won’t let you move on to the next item until you’ve selected the documents you have.
For my license, I needed my passport, out-of-state license, proof of DC residency (cable bill), and SS card (have to have proof of SS). For your car, you need proof of insurance, proof of inspection, and your title (must transfer your title from the state you bought your car).
If you have all the items required, the whole thing takes less than 30 mins. I recommend getting to the DMV an hour before it opens, I got there 45 mins early and was roughly fifth in line. Good luck!