how to add object ?

In a mature engine you will model it in an external application, export it through a plug-in to your engine's runtime format and either bake it into your level geometry in your custom editor or import it singly at runtime.

If you're just learning it's probably just easier to hardcode the vertices and such until you get the hang of the rendering. After that you can spend the time developing a model format or using a pre-existing one and learning to import the stuff in from files.

-me

Being in your state, new to OGL that is, i suggest u hardcode it so you will understand how the matrices move and rotate and transform and stuff....