// Create a Task (it does not start running now)
Task<Int32> t = new Task<Int32>(n => Sum((Int32)n), 1000000000);
// You can start the task sometime later
t.Start();
// Optionally, you can explicitly wait for the task to complete
t.Wait(); // FYI: Overloads exist accepting timeout/CancellationToken
// You can get the result (the Result property internally calls Wait)
Console.WriteLine("The Sum is: " + t.Result); // An Int32 value

Task<Int32> t = new Task<Int32>(n => Sum((Int32)n), 100000000);
t.Start();

t.ContinueWith(task => Console.WriteLine("The sum is: " + task.Result),
TaskContinuationOptions.OnlyOnRanToCompletion);//only completion
t.ContinueWith(task => Console.WriteLine("Sum threw: " + task.Exception),
TaskContinuationOptions.OnlyOnFaulted);//only exception
t.ContinueWith(task => Console.WriteLine("Sum was canceled"),
TaskContinuationOptions.OnlyOnCanceled);//only cencel