Azure App Service enables you to build and host web apps, mobile back ends, and RESTful APIs in the programming language of your choice without managing infrastructure. When you refer Azure Web App, you actually refer the Azure App Service itself.
Azure Mobile Apps SDKs allows you to integrate application with Azure App Service and your mobile application easily.
https://learn.microsoft.com/en-us/azure/developer/mobile-apps/azure-mobile-apps/overview
To understand how you can start with mobile application, you may refer the quickstarts
https://learn.microsoft.com/en-us/azure/developer/mobile-apps/azure-mobile-apps/quickstarts/maui/
Hope this helps