To create a folder, click the + Folder option as shown below.
Give the folder a name, and select the pink 'create' button to continue.
When the new folder is created, select the My Menus tab to return to your list of menus. Drag and drop the menus you would like to add to the new folder on the left.
Click the downward arrow next to the folder name as shown below to rename the folder, or delete the folder (menus saved in the folder will still be saved to your account and stored in the All folder).
Hover your mouse over the image of the menu and click the downward arrow in the corner as shown below to remove the menu from the folder.