On Update

On Update is a field action that triggers a script when a field value is modified. Note that this section is executed only if the field value has been successfully edited.

Go to https://creator.zoho.com/sampleapps/script-actions/#View:On_User_Input_View and edit any record. There is a hidden field that captures the new updated value in its field. Below code was written in the On Update section.
Updated_Value = Choose_any_option;

You may want to send email to the administrator when a field value is modified. In that case, you can write the send mail task in the On Update section of the field.
How to reach the On Update section?
  1. Edit your application (by clicking on Edit this application link, or from the home page, click on the Edit link next to your application)
  2. Select your Form from the Forms tab. 
  3. Mouse hover to the corresponding field and click on “Actions on Update“. That will take you to the script section.
Click on Options (at the top) ->Copy this application to copy the application to your account.