DDP-Client connection with Ios Native app

I want to create chat app with DDP client and ios native.I am successfully connected DDP.But i dont know how to proceed from here.Please let me know how can i send one to one message with DDP.Below are the log i am getting after connectd.

2016-02-05 12:15:21.434 DDPTestSample[3362:1485125] msg is ping
2016-02-05 12:15:53.546 DDPTestSample[3362:1485125] msg is ping