Fortunately, you are not dependent upon theory and diagrams. Take up thy flute, finger xxx xxx and blow softly. You'll get low D, mode 1
Now tighten the embouchure and blow again. You'll get middle D, mode 2.
Tighten some more and blow again. Mode 3, 2nd octave A
Tighten more and try again. Mode 4, 3rd octave D.
Mode 5, if you are that good, will be 3rd octave F#
And so it goes on, in theory forever, but practically limited by the cut-off frequency, a factor of bore and fingerhole diameters, above which the flute becomes very uncooperative. You might have achieved 5 modes on xxx xxx, but try other fingerings. Heh heh heh.....