The program assumes some basic Docker knowledge. One of the best ways of getting up to speed on that is to go over the exercise that was created for Docker's 3rd birthday, this is the link (on github). While the workshop itself does not include (much) practical exercise, it is worthwhile to go over the exercises in advance.
Depending on your background this might take you from 1-4 hours. It would be sufficient to stop at section 4.0 (the challenge) though you are encouraged to dive into that as well!
There is also a great playlist of Docker tutorials on YouTube. In total this amounts to a few hours.