I am providing below a step-by-step approach to use task API with .net clients which I thought would be useful to other users as I didn't find a proper documentation on this yet.

Step1: 

Use the provided task API URL(http://YOURSERVER:8585/services/bizPolicy/taskDotNet) to create a web Reference(Not Service Reference) in visual studio. 

 Step2:        

 You can use the following code on your proxy object created in step1 to pass authentication information.

 CredentialCache cache = new CredentialCache();

  cache.Add( new Uri(proxy.Url), "Basic",new NetworkCredential("Administrator", "manage"));   //you typically pass Administrator level permissions to create the connection and then to use most of the operations

 proxy.Credentials = cache;

Step3:  

Now you can start using the TASK API documentation which will be found in 

Task_Engine_API_and_Service_Reference.pdf ........It has all the information about different operations that you can call from your proxy for achieving different results.

I hope this helps anybody looking to invoke Task API from .NET clients.

Thanks,

Kumar Pindiprolu.