Data Validation is a function provided by Excel to limit users from entering value other than those pre-defined. For example, you might want the user to enter only values between 0 and 200. You can set the limit using this function. In the following example, I have used it to limit users from entering values or text other than those in the list which I have pre-defined.
a. Select the cell in the worksheet where you want to limit user to certain values.
b. Go to Data and select Validation as shown in the figure below:
c. In the dialog box, select the Settings tab. In the validation criteria, "Allow:" section, choose List.
d. In the "source:" section, enter the list of words or phrases allowed, each of them separated by a comma as shown.
e. In the Input Message tab, you can enter a Title or a question and a message for the user.
f. In the Error Alert tab, enter a title and message if the user does not follow your instruction. Click OK and you are done. Now users can only select No and no other answers.