a sample for WF.

gistfile1.cs

internal class Program
{
    private static void Main(string[] args)
    {
        WorkflowInvoker.Invoke(CreateWorkflow());

        Console.ReadKey();
    }

    private static Activity CreateWorkflow()
    {
        Variable<int> numberBells = new Variable<int>()
        {
            Name = "numberBells",
            Default = DateTime.Now.Hour
        };
        Variable<int> counter = new Variable<int>()
        {
            Name = "counter",
            Default = 1
        };
        return new Sequence()
        {
            DisplayName = "Main Sequence",
            Variables = { numberBells, counter },
            Activities =
            {
                new WriteLine(){
                    DisplayName="Hello",
                    Text="Hello World."
                },
                new If(){
                    DisplayName="Adjust for PM",
                    Condition=ExpressionServices.Convert<bool>(env=>numberBells.Get(env)>12),
                    Then=new Assign<int>(){
                        DisplayName="Adjust Bells",
                        To=new OutArgument<int>(numberBells),
                        Value=new InArgument<int>(env=>numberBells.Get(env)-12)
                    }
                },
                new While(){
                    DisplayName="Sound Bells",
                    Condition=ExpressionServices.Convert<bool>(env=>counter.Get(env)<=numberBells.Get(env)),
                    Body=new Sequence(){
                        DisplayName="Sound Bell",
                        Activities={
                            new WriteLine(){
                                Text=new InArgument<string>(env=>counter.Get(env
                                    ).ToString())
                            },
                            new Assign<int>(){
                                DisplayName="Increment Counter",
                                To=new OutArgument<int>(counter),
                                Value=new InArgument<int>(env=>counter.Get(env)+1)
                            },
                            new Delay(){
                                Duration=TimeSpan.FromSeconds(1)
                            }
                        }
                    }
                },
                new WriteLine(){
                    DisplayName="Display Time",
                    Text="The time is "+DateTime.Now.ToString()
                },
                new If(){
                    DisplayName="Greeting",
                    Condition=ExpressionServices.Convert<bool>(env=>DateTime.Now.Hour>=18),
                    Then=new WriteLine(){Text="Good Evening."},
                    Else=new WriteLine(){Text="Good Day."}
                }
            }
        };
    }
}

also, you should involve following three namespaces:
using System.Activities;
using System.Activities.Expressions;
using System.Activities.Statements;