Check out example codes for "hostbuilder add environment variables". It will help you in understanding the concepts better.

Code Example 1

var builder = new HostBuilder();
        builder
        .ConfigureHostConfiguration(config =>
         {
             config.AddEnvironmentVariables(prefix:"DOTNETCORE_");
         })
         .ConfigureAppConfiguration((context, config) =>
         {
             config.AddJsonFile("appsettings.json", optional: false);
             config.AddJsonFile($"appsettings.{context.HostingEnvironment.EnvironmentName}.json", optional: true);
         })

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