Yes, you can definitely create a legend or key for an Excel worksheet. Here's how:

1. First, decide what you want your legend or key to represent. For example, if you have a table of data with different colors representing different categories, you might want to create a legend that explains what each color represents.
   
2. Next, create a new section of your worksheet where you want to place your legend or key. This could be at the top, bottom, or side of your worksheet, depending on your preference.
   
3. In the first cell of your legend or key section, type the name of the first category or item you want to represent. For example, if you're creating a legend for colors, you might type "Red" in the first cell.
   
4. In the cell next to the name of your first category, use the "Fill Color" tool to fill the cell with the color that represents that category. To do this, select the cell, click on the "Fill Color" tool in the "Font" section of the "Home" tab, and choose the color you want.
   
5. Repeat steps 3 and 4 for each additional category or item you want to represent in your legend or key.
   
6. Finally, format your legend or key section as desired. You might want to add a border around the section, change the font size or color, or adjust the column widths to make everything fit nicely.

That's it! Your legend or key is now complete and ready to help readers understand your worksheet.