To make your notes begin and end clearly, you will need to use a technique called tonguing. To get the correct movement for tonguing, say “taa”. Do this several times and notice how your tongue starts against the back of your top teeth and then withdraws to let air through as you say taa.
Next, place the flute in position against your lip and repeat the taa movement with your tongue. This will cause the note to start clearly. To stop the note, place your tongue back against your top teeth.