RS asks:

“could u please explain me what is earth’s [wiki]magnetic field[/wiki]? in detail and easily in brief?”

Ans

Please refer to http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magearth.html for details. If you have any specific doubts related to it please ask as comment here.

Also see http://en.wikipedia.org/wiki/Earth’s_magnetic_field

[wiki]Geomagnetism[/wiki]