The left-hand sidebar allows you to quickly jump to different sections of your Workflowy and also drag and drop items from the current document to a new location.
You can click on the hamburger icon in the top-left side of the menu bar to toggle the sidebar.
If the sidebar is already visible, you can click on the arrow icon to hide it.
The STARRED section
The left-hand sidebar has two main parts, the first is the 'STARRED' section that shows all your starred items and searches. This is where you can click on the items to navigate to them or un-star them.
The HOME section
The second section is the 'HOME' section. This is where you'll find the entire layout of your Workflowy. You can use this section to navigate within your Workflowy or add items.