I am a clarinet player but I have bought a Yamaha flute because it was ridiculously cheap. I can play the low register just fine but I have problems playing the second register. The clarinet has a register key played with the left thumb which automatically put you into the second register. The flute doesn't have such a key (at least, mine doesn't). So, my beginners question is, how do you play above the low register ? No doubt this will seem simple to you flutists.

By pushing more air through the instrument and adjusting your embouchure you can reach the next octave. Begin by playing the lowest note you can play and work your way up gradually; eventually you should be able to get it.

practice, practice, practice. Eventually your embrochure will learn to adjust itself naturally for those octaves. Until then, buy some earmuffs. =)