The Field Update option helps you to automatically update certain field values in the records, when the associated workflow rule is triggered.
To create field updates:
Click Setup > Automation > Workflow > Field Updates.
In the Workflow Field Updates page, click Configure Field Update.
In the New Workflow Field Update page, do the following:
Enter a Name for the field update.
Select the Module from the drop-down list.
You can also update the field values of the related parent records associated to the record selected for workflow rule. For example: While creating workflow rules for Contacts, you will be able to update the fields of the parent Client records too.
Select the field from the Update drop-down list that needs to be updated.
Specify the value for the field that you want updated.
Workflow Field Updates cannot be associated to a workflow rule if the Execution Criteria selected for a rule is 'Delete'.
You can associate a maximum of 3 field updates to each action (Instant and Time Based Actions).
You can update the Record Owner field too using this feature.
From within a workflow rule, you can also create Workflow Field Updates to update parent record's fields.