You might have noticed that Gmail tends to collapse a number of folders from the side panel. If you check these folders frequently, you probably want to keep them just one click away on the left side of your screen.
Here’s how to unhide folders in Gmail.
Click on the settings cog (top right) and go toSee all settings.
Navigate to Labels and from the Show in label listcolumn select show for every folder that you want to keep in the side panel. You also have the option to show a folder only if it contains unread emails.