Validation rules ensure that data conforms to certain standards. And these validation rules do involve writing some code. I walk you through examples of validation rules in practice, and how to display and place error messages when data does not comply.
I've also included a helpful resource to sample validation rules that you can pull from to get started with writing out your own validation rules. I also cover scenarios of when validation rules will fire, in addition to user entry. These scenarios may appear on your admin exam, such as:
Field Updates Via the Data Loader
Field Updates Via API Calls
Field Updates on Fields Hidden in Page Layouts (via workflow rules and field updates)
Sample Validation Rules - https://help.salesforce.com/articleView?id=fields_useful_field_validation_formulas.htm&type=5