For configuring a Web App in Azure, first we need to create an App Service Plan.
App Service Plan can be created from DevOps --> Serverless --> App Service Plan.
Refer below for the sample App Service Plan.
Create Web App
Once we have App Service Plan, Create a Web App Resource. App Service Plan can be created with Publish option as Code or Docker.
A list of the platform (NodeJs, python, etc) is available when Publish value as Code is selected. If Publish as Docker is selected, the User needs to enter the Docker Image to configure for creating a web app.