Start screen is the first screen of Excel, when you open Excel application. Below image shows Start screen in Excel 2019.
Excel Start Screen is divided into two panels; 1) Left panel and 2) Right panel
Excel Start Screen - Left Panel
The Left panel (which is green in color) contains a list of recently opened Excel files. Below the list of recently opened Excel files, there is a link "Open Other workbooks". If you click "Open Other workbooks", Excel will take you to the Backstage view, where you can open an existing Excel document.
Excel Start Screen - Right Panel
The most important button on Right panel is labelled as "Blank workbook". By clicking the "Blank workbook" button, you can open a new blank Excel workbook.
Excel Start Screen's Right panel also contains a tour to Excel, Tutorials for formulas and functions and tutorials for pivot tables.
A list of templates is also available in Excel Start Screen's Right panel. You can use these templates as the basis of your Excel document.
Right panel of Start screen includes a text box, using which you can search for Excel templates online too.
There is also a link in top right corner Excel Start Screen, that you can use to login to your Microsoft account.