Design Mode is a feature in Excel that allows you to edit and customize the controls and objects on a worksheet. When you activate Design Mode, you can add, delete, or modify form controls, ActiveX controls, and other objects on your worksheet.

To activate Design Mode, you can follow these steps:

1. Click on the Developer tab in the Excel ribbon. If you don't see the Developer tab, you may need to enable it in Excel Options.
2. In the Controls group, click on the Design Mode button. This will activate Design Mode and allow you to edit the controls and objects on your worksheet.

When you are in Design Mode, you can select and modify various controls and objects on your worksheet. For example, you can resize a button, change the font size of a label, or add a new form control to your worksheet.

Design Mode is particularly useful when you are creating custom forms or user interfaces in Excel. By using form controls and ActiveX controls, you can create interactive worksheets that allow users to input data, make selections, and perform calculations.

In summary, Design Mode is a powerful feature in Excel that allows you to customize and edit the controls and objects on your worksheet. It is particularly useful when you are creating custom forms or user interfaces in Excel.