The left hand column of the edit proposal screen shows all the current sections of your sales quote.
A section is like a chapter and you can have as few or as many as you choose. Templates often will contain a base set of sections but you can freely add/delete or even re-arrange these sections. To re-arrange a section simply drag and drop it in the new position.
To add a new section click the Add Section button (the button is below the list of sections on the left of the screen).
Once a new section has been created you can give it an appropriate title and start adding content.
Content can be added manually using the + Insert buttons or from the content libraries on the right.
Once you have added a new section, it will be displayed in the left column. You can also navigate to each proposal section by clicking on it.