How can a case be created from an activity? | MS Dynamics CRM

Case can be created from a Fax, Phone Call, Email, Letter, or Appointment activity. Following are the steps to create a case from an activity:
=>   Select the activity from which the case is to be created.
=>     Select the Convert activity to a Case option from the Action toolbar.
=>    Select the name of the Customer with which the case is to be created in the Lookup.