How are workflows organized?

Workflows are organized into stages, tasks and steps.  Each workflow has 4 stages:  Lead, Opportunity, Account and Install.  (Note:  The name and number of stages cannot be changed.)  And under each stage are tasks with names that can be changed.  You always have the option to add more tasks. 

Also, within each task, you can add multiple steps such as activities to complete and documents to upload.  You can also make steps mandatory, so they must be completed before the user can move on to the next task or stage.