The customer service page is the page containing the FAQs (Frequently Asked Questions). You can find it by navigating to SERVICES > FAQ in the left menu of the back office. By clicking green plus icon in the navigation at the top of the screen, you can add a category and create its associated questions and their answers.
If you also want to add additional informative text(s), navigate to SERVICE > Text pages in the left menu and click the Customer service page. You will then be taken to its editing environment. All text(s) entered here will be displayed above the FAQ section of the customer service page of your online store.