Can anyone explain difference between levels and curves regarding luminance in Photoshop?? As the both of them affects the whites blacks and their intensities ,then what is the difference between them?
In both tools you are mapping the existing levels to new levels.
Levels is simply a straight line from lowest level to highest level. You can adjust the start point, end point and slope of the line.
Curves are more sophisticated.
You can adjust the start and end points, but you can also shape the curve to whatever you want.
Curves allows much more flexibility and control. Experiment is the best way to get a feel for this.
Here is a demonstration of the difference between Levels and Curves, showing action of both. http://www.scantips.com/curve/
Both do the same thing, but Levels is just a small subset of what Curves can do.