Hello Sumant,
What you're asking is a very general question. DAQ or Data Acquisition is a pretty big topic.
Is there a specific device or signal you're working with?
NI has a number of courses available:
http://www.ni.com/training/daq.htm
Here's an introduction to DAQ:
http://zone.ni.com/devzone/cda/tut/p/id/3536
Nice tutorial:
http://www.ni.com/swf/presentation/us/labview/aap/default.htm