How to rotate a specific object in openGL?

Tutorial #4 from NeHe shows how to do that precisely.

Also, you might want to take a look at this:

OpenGL Rotation

You need the rotation to be in effect only when the geometry you're interested in is being drawn.

... draw stuff ...
glPushMatrix();
glRotatef(angle, 0, 1, 0);
... draw rotated stuff ...
glPopMatrix();
... draw more stuff ...