Azure App Service is a logical container which contains all the resources to build the Website, Mobile App and Service Apps. You can quickly build the robust websites with your choice technologies.
You can choose your desired OS type to build and host the web app of your preferred technologies.
Currently MS Azure supports the Windows and Linux OS
And you can build websites or web apps by choosing any one of the following programmings.
.NET, Node.js, PHP, Python (only for linux), Java, HTML 5 and Custom windows container (Docker - Preview)
To understand further on what is Azure App Service.
Consider you have the simple website which hosted with 3rd party hosting company.Its your choice to go the shared hosting option or Dedicated hosting.
Please see the attached study materials for the details of App Service Plans. You have to choose as per your business requirement and capacity plan.
For exam question, You have to understood all these pricing details of the App Service offered by Microsoft.
Question can be expected what plan you could suggest your client, and what features especially "Instances for auto scaling , Hybrid connectivity , Network isolation for critical application and Disk space required for your application.
To manage and up and running your website they need below resources.
DNS
Physical Server with Server technologies (IIS , IIS Express or Apache)
Server hardware and software with latest patches and updates
For your website,
It must have the physical file systems on the server with authentication and authorization option to protect your web contents.
And also need FTP to updates the web contents.
Now you don't worry about all these features, MS Azure will take care of it automatically. So you can focus only on the website development.
This logical container also useful to Microsoft for categorizing the hosting packages and convenient way for billing the consumer.