The first thing you need to do is make sure that you have the NI-DAQmx driver installed. This should've came with your device, but if not you can download it from ni.com/updates. After the driver is installed it will add examples for LabWindows CVI. In LabWindows CVI you can go to Help » Find Examples to open the NI Example Finder and then navigate to Hardware Input and Output » DAQmx » Generating Digital Pulses. There is a DigPulse.prj which will show you how to create a digital pulse with a specific pulse width. There is also a project called DigPulseTrain-Cont-DigStart.prj that you can look at to see how to implement a digital start trigger. Take a look at these and let me know if you have any additional questions.
