With all those tools that Salesforce provides us with, it's sometimes not that easy to decide which tool to use.
As a rule of thumb, if you can solve your business requirement with declarative features, then use declarative features. They are faster to create than coding, easier to manage and maintain by administrators in the future, and don't require a developer to create or modify them.
Apex classes and triggers offer greater flexibility and full control, but they are harder to create and maintain, and will always require a developer. But hey, don't let that stop you, as you will be able to do this yourself after reading this book, right?
For the exam, learn the comparison chart, by heart, that you can find in the Common use cases for declarative customization section of Chapter 1, Salesforce Fundamentals...
