C#: How do you work with configuration?

1var builder = WebApplication.CreateBuilder(args);
2var config = builder.Configuration;
3
4var connectionString = config["ConnectionStrings:Default"];
5var port = config.GetValue<int>("Port");

1builder.Services.Configure<Settings>(
2    builder.Configuration.GetSection("Settings"));
3
4public class Settings
5{
6    public string ApiKey { get; set; }
7}