在使用Autofac注册事务时，可以按照以下步骤进行操作：

1. 首先，确保已经安装了Autofac和Autofac.Extensions.DependencyInjection NuGet包。

2. 创建一个TransactionModule类，该类继承自Autofac.Module类，并在其中注册事务相关的组件。

using System;
using System.Data;
using System.Data.Common;
using System.Data.SqlClient;
using Autofac;
using Autofac.Core;

namespace YourNamespace
{
    public class TransactionModule : Module
    {
        protected override void Load(ContainerBuilder builder)
        {
            builder.Register((c, p) =>
            {
                var connectionString = "YourConnectionString";
                var dbProviderFactory = DbProviderFactories.GetFactory("System.Data.SqlClient");
                var connection = dbProviderFactory.CreateConnection();
                connection.ConnectionString = connectionString;

                return connection;
            }).As().InstancePerLifetimeScope();

            builder.Register((c, p) =>
            {
                var connection = c.Resolve();
                var transaction = connection.BeginTransaction();

                return transaction;
            }).As().InstancePerLifetimeScope();

            builder.RegisterAssemblyTypes(typeof(YourRepositoryClass).Assembly)
                   .Where(t => t.Name.EndsWith("Repository"))
                   .AsImplementedInterfaces()
                   .InstancePerLifetimeScope();
        }
    }
}

3. 在Startup类的ConfigureServices方法中，注册AutofacContainerBuilder，并将TransactionModule添加到容器中。

using Autofac;
using Autofac.Extensions.DependencyInjection;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;

namespace YourNamespace
{
    public class Startup
    {
        public IConfiguration Configuration { get; }

        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IServiceProvider ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();

            var containerBuilder = new ContainerBuilder();
            containerBuilder.RegisterModule(new TransactionModule());
            containerBuilder.Populate(services);

            var container = containerBuilder.Build();
            return new AutofacServiceProvider(container);
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            // ...
        }
    }
}

4. 在需要使用事务的类中注入IDbTransaction，然后使用该事务进行数据库操作。

using System;
using System.Data;

namespace YourNamespace
{
    public class YourRepositoryClass : IYourRepositoryInterface
    {
        private readonly IDbTransaction _transaction;

        public YourRepositoryClass(IDbTransaction transaction)
        {
            _transaction = transaction ?? throw new ArgumentNullException(nameof(transaction));
        }

        public void InsertData()
        {
            // 使用 _transaction 执行数据库操作
        }
    }
}

通过以上步骤，就可以在项目中使用Autofac注册事务，实现数据库操作的事务控制。