It's easy to start a new document whenever you feel inspired. When you navigate the dashboard, there is always a green plus sign button in the top right corner. Click that, and select "Add Document" from the drop-down list.
Be sure to name your document before navigating away, because all documents will automatically save, and you want to be able to easily find them later.
You can find your new documents in the Documents tab on the sidebar, or you can search by name from the home screen. See for yourself below: