hi everyone!
im a newbie here…i just want to learn how to model 3D object in openGL because i just know to make the 2D object only using openGL…i just want to explore
You need a 3D modeller, like Blender (open source) or Maya 3D 
I prefere Blender ^^
Then you need a exporter (for Blender / Maya 3D / …) and a suitable importer for OpenGL + C++/C#
You can use common formats (like .md2 (Quake II Model) or .obj (Wafefront Object) for starting),
or you use your own fomat, as I do 
These classes manage your created object and are capable to draw it.
But first you should work into a 3D-modeller 