Git is a source control tool. It is for versioning of source code to Git-based systems like Github and Azure DevOps. It has nothing to do with publishing web apps.
Publishing web apps involves a completely different toolset depending upon what you're publishing. If you're building an ASP.NET app then you might be using msdeploy
or dotnet publish
depending upon the framework. If you're building a typescript, Angular or Nodejs app then you're using completely different sets of tools.
If you're using Visual Studio to deploy apps then you're using the Publish menu item.
If you are using Git Actions then you might be able to configure an action to publish your app once it is pushed to Github but that is not a Azure Webapps issue.
If you're using an Azure-based tool to publish your app then please provide us more context. Most likely you haven't configured your tooling to deploy to your app, you haven't set up your Azure subscription, resource group, app service and credentials to deploy the app yet or you have a permissions problem. At this point we are completely guessing at which of the many different configuration and toolsets you may be using here. Please provide us lots more information including any relevant configuration settings and log messages.