Folders allow you to organize your various Messages in a way that makes sense to you, beyond the standard Inbox. To move a Message (or Messages) from the Inbox into a folder, you will want to select the checkbox for that Message and use the “Bulk Action” dropdown to select “Archive To Folder”. From there, you will have the option to select a pre-existing folder or, optionally, you can create a new folder directly from this menu by selecting “Create Folder” entering your desired folder name, and clicking “Add”.
To manage existing folders simply hover over the folder in the left-side menu. This will bring up two buttons allowing you to rename or delete the folder. It is important to note that if you delete a folder that contains Messages those Messages will be moved to your inbox after the folder is deleted.