The sidebar is the area to the right of your spreadsheet that shows either the Format inspector or the Organize controls.
Format: Click in the toolbar to show formatting controls for whatever is selected in the spreadsheet, like a table, chart, text, or a shape. Click the tabs at the top of the sidebar to see more controls.
Organize: Click in the toolbar to show controls for creating sorting rule, filtering, and categories for the spreadsheet.
If a sidebar is open and you click its icon in the toolbar, the sidebar closes.