An Excel drop down list can be created using the Excel data validation options as follows:
Enter your allowed values (i.e. the values that you want to appear in the drop-down list) into any column of your spreadsheet (e.g. cells A1 to A10).
Select the cell (or cells) that you want the drop-down list to appear in (we have selected cell C2 in the above example on the right).
From the Data tab on your Excel spreadsheet ribbon, select Data Validation→Data Validation...
The Data Validation dialog box will appear. Within this dialog box:
In the Source field, enter the range of cells where you typed in your original list of options (e.g. $A$1:$A$10).
If you prefer, you can enter this range using the mouse, by clicking on the symbol at the right of the Source field and then selecting the required range of cells with the mouse.The selected cell should now contain a drop-down menu containing your list of allowed values.
To tidy up the spreadsheet, you might want to hide the column that contains the orignal list.
The resulting spreadsheet (with column A hidden) is shown aboveon the left.