my project has no Startup.cs file, only Program.cs

It seems like you're working with a .NET Core 3.x or .NET 5+ project. In these versions, the startup configurations are handled in the Program.cs file, not in a separate Startup.cs file. Here's a step-by-step guide on how to set up your configurations:

1. Open your Program.cs file. You should see a Main method which creates and runs a Host. The Host is what will host your application, and it is configured in this method.

2. To configure services, you can call the ConfigureServices method on the IHostBuilder instance. This method takes a HostBuilderContext and an IServiceCollection as parameters. You can add services to the IServiceCollection in the same way you would in the ConfigureServices method in Startup.cs.

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureServices((hostContext, services) =>
        {
            services.AddRazorPages();
        });

3. To configure the HTTP request pipeline, you can call the Configure method on the IApplicationBuilder instance. This method takes an IApplicationBuilder, IWebHostEnvironment, and ILogger as parameters. You can configure the pipeline in the same way you would in the Configure method in Startup.cs.

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.Configure((context, builder) =>
            {
                if (context.HostingEnvironment.IsDevelopment())
                {
                    builder.UseDeveloperExceptionPage();
                }
                else
                {
                    builder.UseExceptionHandler("/Home/Error");
                    builder.UseHsts();
                }

                builder.UseHttpsRedirection();
                builder.UseStaticFiles();

                builder.UseRouting();

                builder.UseAuthorization();

                builder.UseEndpoints(endpoints =>
                {
                    endpoints.MapControllerRoute(
                        name: "default",
                        pattern: "{controller=Home}/{action=Index}/{id?}");
                });
            });
        });

4. If you need to add more configurations, you can do so by adding more methods to the IHostBuilder instance in the Main method.

Remember, the Program.cs file in .NET Core 3.x and .NET 5+ is equivalent to the Startup.cs file in previous versions. All the configurations you would normally do in Startup.cs can be done in Program.cs.