Hi,
how to know the normals are pointing in the right direction in the 3d object ? ops:

You can turn on normal display in the viewport (right toolbar, circle-with-stick icon about halfway down, “Display Normals”).

no no …….In some tutorial I have seen that we need to check the normals are pointing in the right direction otherwise we have to reverse it and that will be very useful for materials…….In this case how I can know that normals are pointing in right direction.

What twod said is correct - turn on Normal display as described and you should see a bunch of little normal lines appear. The direction they are pointing in shows the direction of your normals. If they are on the outside of your geometry, like hairs, then they are in the right direction. If they appear on the inside then they are in the wrong direction.

What is the tutorial you're using? - if I know exactly what they're talking about I might be able to help more.

thx deselby , but I have come across the tutorial in youtube , if u please the image demonstration would give a clear view. :roll:

What you mean by Normal facing right diraction??
Normals are always perpendicular to tangent. But of course you can modify it. If you have some funky Normals because of noise on object or some other modification then can always use facet to post compute normals.

We need to be careful here to differentiate between point and primitive normals.

I have a hunch that the original poster actually needs to see the primitive normals (Display primitive normals -button), not point normals (Display normals -button).

Point normal data is just a per-point attribute that can have any values the user wants.

Primitive normal data is intrinsic to the polygon, it is determined by vertex locations and winding. The only way to change the primitive normals without changing the geometry is by reversing the winding (with Reverse SOP as the original posted hinted at), which negates the direction of the primitive normals.

TL;DR - You need to switch on Display primitive normals.