By default LibreOffice displays three sheets "Sheet1" to "Sheet3", in each new spreadsheet. You can switch between sheets in a spreadsheet using the sheet tabs at the bottom of the screen.
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 forwards and backwards through all sheet tabs. To display the sheet itself click on the sheet tab.