The Items Panel is visible in all modes except Component mode.
When in Config mode, it will show all known Snippets. Buttons to add, edit and delete Snippets will also be shown.
When in the other modes it will display either Components, Modules or Device Panels along with their names and descriptions. These can be dragged and dropped onto the Canvas. It will also show a search box where text can be entered to filter the displayed items if the name or description of the item contains the text.