The More button on the sidebar allows you to navigate all your folders and subfolders. It gives you quick access to needed folders without cluttering your sidebar.

When you open a folder, it appears in the Recents section at the bottom of the sidebar. You can quickly access it anytime.

The Favorites section on the sidebar allows you to pin your main folders:

1. Click More.
2. Choose the folder you want to pin and click on the star icon.
   

3. You can color-code the folder you added. Right-click on the folder on the sidebar and select Change Folder Color.
4. To reorder folders within the Favorites section, simply drag & drop them.

To pin a system folder (like Shared, Snoozed, Reminders):

1. Click More and select the needed folder.
2. Right-click on the folder on the sidebar and select Move to Favorites. Alternatively, you can drag & drop this folder anywhere you wish.

Here is the alternative way to add folders to the sidebar:

1. Click Spark at the top left of your screen.
2. Open Preferences > Folders.
3. Tick the folders you wish to keep on the sidebar.

Right-click on the folder on the sidebar and select Remove from Sidebar.

If you have multiple folders in the Recents section on the sidebar, click Clear to remove them all at once.