Views 2 'concept' question

I'm a little bewildered by Views 2 (and Views 1) ....but think it is immensly powerful, so it would help to really understand it.

I've viewed Mastering Drupal's Views 2 screencast http://www.masteringdrupal.com/screencast/new-features-in-views2/play and tried following the outline at http://drupal.org/node/168752#comment-263585 (5.x) to create a random testimonial view...and while it was a great overview, I'm still missing a fundamental concept.

It seems like each View requires certain things, to be added/created. Everything else is optional, or just part of the configuration.

I'm not clear on what is required? ie: Are Fields required? Are Arguments, Relationships, etc, etc required?

For example, the 'random testimonial' view I created (using D5 instructions) gives me the following warning:
Display Defaults has no access control but does not contain a filter for published nodes.

I'm less concerned about the warning....and more interested in fundamentally understanding 'what steps are needed to create a view' - one its created, I can monkey with the configuration to my liking.

Any help would be greatly appreciated.

kwg