Plume comes with main sidebar (Primary sidebar) and Footer widget columns but if you want to create more than that you can by adding the sidebar name into the text field, click on + ADD NEW SIDEBAR button and click on save changes to save the new sidebar, after that navigate to Appearance > Widgets and start adding your widgets into that sidebar.

Sidebars could be used from different location like Pages, Theme options (Blog, WooCommerce or Search)