The effect of many OpenGL functions depends on whether a particular mode is in effect. The glEnable and glDisable functions set such modes; glIsEnabled determines whether a particular mode is set.
You can control the execution of previously issued OpenGL functions with glFinish, which forces all such functions to finish, or glFlush, which ensures that all such functions will be completed in a finite time.
In a particular implementation of OpenGL, you may be able to control certain behaviors with hints by using glHint. Such behaviors are the quality of color and texture coordinate interpolation; the accuracy of fog calculations; and the sampling quality of antialiased points, lines, or polygons.