Face orientation

[Omar_Sakr]

I can not understand the importance of face oreintation.
can any one help?

[Medial]

There are several issues with face orientation.
First - most render engines dont show back of the faces - face from behind is 100% transparent, so for example mesh exported to Unity or Unreal with wrong orientation will render in very strange way.
Blender shows both sides, but it might display wrong texture if its textured - the image willl be mirrored, like seen from behind.

And probably most important for internal work in blender, blender modifiers use face orientation to perform operations, so with wrong orientation most of modifiers will work wrong.

[Omar_Sakr]

Thanks!