Can we display text using opengl?
Yes you can, you can create text as bitmaps and place them on polygons as textures.
On Windows you can use wglCreateFontOulines and another function to create displaylists of bitmap or polygon text, you can then draw text by calling glCallLists(). X has a similair function.
There also exists some libraries that use FreeType to render text (GLTT just to name one).
So there are a number of solutions, it all dependes on what you want to use the text for and how you want to display it, just like ordinary 2D text or in 3D.
Hope that helps