Before you add the complexity of the keys you will learn how to make a sound on just the head joint. Remove you head joint from your flute. Bring the head joint up so that your mouth lines up with the embouchure plate. Next, you will want to cover the open end of the head joint with your hand. Since the flute works by air blowing across the head joint, not into it, you will still be able to make a sound.
Bring your lips close to the embouchure hole and blow across it as if you were saying “tuuuuuuuu”.
It will take time before you can get a clean sound. See how long you can sustain the tone before it dies off.