A Workflow Container page acts as the manager of one or more child Workflow pages; aside from naming the Workflow Container, there isn't much more you do with it specifically.
Workflow Web Pages provide a task-specific usability improvement for typical Screen-based applications. Confusion caused by large, busy screens is avoided, since portions of a screen can be included in each step (only those fields relevant to a step in the task being performed).
Since each Workflow page acts as a composite page, it can contain just a portion of a single screen, or portions of multiple screens, which allows you to re-organize the fields the user works with based on the job you are modeling, not the design of the screens.
Informational pages can be inserted into the flow, so that after entering a set of fields, the user can be provided with some "inter-step" help on what is going to happen next.
All navigation between screens is automatically handled by the framework--the UI ASPX pages that are generated can be freely modified and juiced-up to help even more with usability.