You can use the TODAY() or NOW() function to insert the current date and time into an Excel worksheet. You can also use the shortcut CTRL+; to insert the date and time. Here are some steps to help you use the functions effectively:

1. Insert the date or time cell by typing =TODAY() or =NOW().
2. Select the formatting icon (below the cell) and choose the type of date or time you want to display.
3. Refresh the cell every time you reopen the workbook by pressing F9.
4. Use the shortcut CTRL+; to insert the date and time into any part of the worksheet.