Why do magnetic field lines go from North to South? Why magnetic lines comes from north to south out side of the magnet 
is any magnetic lines comes from south to north if so in which direction 
What is the reason of magnetic lineS 
 A: Making magnetic field lines go from north to south is just a convention. An equally valid convention could have been magnetic field lines going from south to north. The magnetic field lines are a conceptual tool to visualize the magnetic field. 
An interesting point about magnetic fields is that they are divergenceless (i.e. $\nabla\cdot\vec{B}=0$). What this means is that the elementary unit that gives a static magnetic field is a dipole (e.g. a bar magnet).   
A: A picture is worth a thousand words.

Iron filings display the "lines", like small dipoles as @PhysGrad has mentioned. The compasses are larger dipoles and the permanent magnet itself is the largest. One can imagine tiny dipoles following "lines", so in a sense they exist to the accuracy of the experiment.
The image displays the need for a convention , one could call it red and blue poles.
Actually the convention is a bit bizarre  it was adopted by watching a compass pointing to earth's north, which makes the  magnet  in the north pole a south magnetic pole!
A: There aren't really magnetic lines - they are maps of the magnetic field. It's just like a contor line map (http://en.wikipedia.org/wiki/Contour_line).
The north end and south end are arbitrary names.
A: *

*By convention.

*If the magnetic line refers to the visualization of B-field, it actually goes from south to north inside a magnet, and north to south outside the magnet. This is because B-field is divergenceless, and consequently magnetic lines are closed loops.

*Magnetic lines are just visualization of magnetic field. They are not "real" lines. In fact, magnetic field permeates space, not just where you draw the line.

