You should first go to
http://zone.ni.com/devzone/cda/tut/p/id/5434 and learn the basics of DAQmx. That should answer your questions but in order to take a single sample, you just use the DAQmx Read set to NChan 1Samp. And, just like traditional DAQ, you can acquire multiple channels with a single task. You specify the channels as Dev1/ai0:4 for example.
