History
The last brief section of this workflow chapter is about the History panel. The History panel tracks all of the individual changes you make over the course of either a session or the entire length of a project. Each change is recorded as an entry in a list with the earliest or oldest entry at the top of the list.
Usually, I typically just track the history of a session, and this is the default behavior. I have never had the need to track every single change in a complete project. If you do want to track your changes throughout the entire length of your project, go to File | Save history with document. This will save everything you do over the course of your project, including access to history before closing and reopening the document.
The History panel basically allows you to scroll through time back to the beginning of a session, or to the very beginning of the creation of the project if you are saving your history with the document. To go back to a certain point...