I want how to use Trigger/Function in Stream Analytics Query of Microsoft Azure ? ..

I want to know how use trigger/function in stream analytics query of Microsoft Azure .I have scenario where there will be continuous flow of events to Event Hub(Event Hub namespace) which will be input to our stream analytics query , example events will be from login to logout and no idea when the logout event happens for a device(unique) , but at the same time there could be flow of multiple(many) such devices-events(login to logoff) happening .Need to calculate the duration time from login to logoff and count of transactions if happens in between login to logoff events for each such device( when login happens at a device , there will be a unique token key generated . I have not provided a detailed description and have not uploaded any files.