Here is a link to an instrument drivers for your device. This can be found by searching ni.com/idnet. See this link for several tutorials that discuss instrument drivers. Here is a link to the E4440A manual. See chapter 4 for commands that can be sent to the device. Since there is instrument drivers for this device, you won't necessarily need to know these commands to program your device with LabVIEW. The instrument drivers use these commands underneath and have put these commands within subVIs to create VIs to perform each action. I hope this helps!