Could someone explain me perpendicular and parallel axis ????

The

parallel axis theorem is probably the most used of the two. It is designed to make the calculation of the moment of inertia easier. The moment of inertia of an object through an axis that contains the center of mass is generally easy to find, at least in a Physics class. The parallel axis theorem deals with an axis parallel to that. Probably the easiest to see clearly is the moment of inertia of a disk about an axis through one edge. We find the moment of inertia of the disk through the CM and use the parallel axis theorem to "shift" the axis to the one on the edge.

The

perpendicular axis theorem is less used, because of the high degree of symmetry needed. The link I showed is pretty much the only kind of circumstance you'll run into.

Both of these, of course, can be calculated numerically.

-Dan