The definition of a workflow, according to Wikipedia, is a "depiction of a sequence of operations". When taken at face value, a workflow is typically something you want to automate in Drupal. In other words, what we're talking about is Drupal Automation and my guess is, you'll want to automate things in Drupal based on certain events.
The confusing part of Drupal automation is the fact that you need to know what works together to accomplish such automation. With the modules of Workflow, Actions*, Triggers* (* Part of Drupal 6 core) and Rules, it can be quite confusing when it comes to automation.
Put simply, in Drupal 6, you can still use the Workflow module (which I don't show in the video) but you can also get by with the default Triggers and Actions (as mentioned, already installed with Drupal). However, unless you know you need to install Workflow module to achieve the automation you're seeking, and potentially install Triggerunlock module (which you don't really need if you install Workflow in Drupal 6), things can get really confusing, really fast.
So, aside from trying to confuse you with the above paragraph (I did that on purpose), about all the setup and things you do or don't need, I focused a bit more on the Rules module because it's a one-stop-shop for automation which goes beyond what you can do with Triggers, Actions and Workflow.
Even though I'm a convert to Drupal's Rules module, my compliments go out to John VanDyk (whose book helped me learn Drupal even better) for creating Workflow and Actions (which I started with in Drupal 4.7) and to Wolfgang Ziegler for creating the ever powerful Rules module. I can only hope this video will provide you with most everything you need to know to automate things so you can achieve your ultimate Drupal workflow!
Note: If you're still working with Drupal 5, then Workflow, Actions, and Workflow-Ng (also by Wolfgang) will give you the automation you need. In most all cases, you'll definitely want Token module installed so you can do the cool stuff the big boys do.