Composer.cs

namespace MyNamespace 
{
  [ComposeAfter(typeof(TeaCommerceComposer))]
  public class MyComposer : IUserComposer 
  {
    public void Compose(Composition composition) 
    {
      composition.WithOrderCheckoutPipeline()
        .InsertBefore<CalculateShippingTask, MyPipelineTask>()
        .Append<MyOtherPipelineTask>();
    }
  }
}

MyPipelineTasks.cs

namespace MyNamespace 
{
  public class MyPipelineTask : PipelineTaskBase<Order> 
  {
    public override PipelineResult<Order> Execute(PipelineContext<Order> context) 
    {
      // Modify the order object or perform some logic.
      context.Data.StringProp = "New Value";
      return Ok();
    }
  }
  public class MyOtherPipelineTask : PipelineTaskBase<Order> 
  {
    public override PipelineResult<Order> Execute(PipelineContext<Order> context) 
    {
      // Modify the order object or perform some logic.
      if (context.Data.BoolProp) {
        return Fail(new PipelineException("Something went wrong"));
      } else {
        return Ok();
      }
    }
  }
}