By default LibreOffice displays one sheet "Sheet1" in each new spreadsheet document. You can add sheets using the (+) button at the bottom of the screen and switch between sheets in a spreadsheet using the sheet tabs.
If the sheet tabs are not visible, choose to display them at the bottom of the screen.
The navigation buttons are enabled when the number of sheets in the document is greater that the number of sheets displayed in the sheet navigation bar.
Use the navigation buttons to display all the sheets belonging to your document. Clicking the button on the far left or the far right displays, respectively, the first or last sheet tab. The middle buttons allow the user to scroll forward and backward through all sheet tabs. To display the sheet itself click on the sheet tab.
Left click: Adds a new empty sheet to the right of the current sheet.
Right click: Opens a sub menu with all sheets not marked hidden. Click on a sheet name to jump to it. Hidden sheets are not listed in the sub menu.