Creating a project

mkdir ftpserver
cd ftpserver
dotnet new console

Adding the NuGet packages

# For dependency injection support (required)
dotnet add package Microsoft.Extensions.DependencyInjection

# For the main FTP server
dotnet add package FubarDev.FtpServer

# For the System.IO-based file system access
dotnet add package FubarDev.FtpServer.FileSystem.DotNet

Using the FTP server

Change your Program.cs to the following code:

using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

using FubarDev.FtpServer;
using FubarDev.FtpServer.FileSystem.DotNet;

using Microsoft.Extensions.DependencyInjection;

namespace QuickStart
{
    class Program
    {
        static async Task Main(string[] args)
        {
            // Setup dependency injection
            var services = new ServiceCollection();

            // use %TEMP%/TestFtpServer as root folder
            services.Configure<DotNetFileSystemOptions>(opt => opt
                .RootPath = Path.Combine(Path.GetTempPath(), "TestFtpServer"));

            // Add FTP server services
            // DotNetFileSystemProvider = Use the .NET file system functionality
            // AnonymousMembershipProvider = allow only anonymous logins
            services.AddFtpServer(builder => builder
                .UseDotNetFileSystem() // Use the .NET file system functionality
                .EnableAnonymousAuthentication()); // allow anonymous logins

            // Configure the FTP server
            services.Configure<FtpServerOptions>(opt => opt.ServerAddress = "127.0.0.1");

            // Build the service provider
            using (var serviceProvider = services.BuildServiceProvider())
            {
                // Initialize the FTP server
                var ftpServerHost = serviceProvider.GetRequiredService<IFtpServerHost>();

                // Start the FTP server
                await ftpServerHost.StartAsync();

                Console.WriteLine("Press ENTER/RETURN to close the test application.");
                Console.ReadLine();

                // Stop the FTP server
                await ftpServerHost.StopAsync();
            }
        }
    }
}

Starting the FTP server

dotnet run

Now your FTP server should be accessible at 127.0.0.1:21.