O.k first probobly the most asked question about flute Ever! Vibrato.... I can make a vibrato but I use my throat and its like I'm huffing as I play, it works but my teacher teaches diaphram ( I know I spelled it wrong)vibrato and I'm not having much luck, does it really matter?

also I need a concerto for a competition and I just started with bloch modale and I've got 3 of 4 movements down but I'm looking for others too, and suggestions for me?

Vibrato is not done with the diaphragm. This muscle acts when you inhale the air. Actually it's done with the abdominal muscles. If you blow air very hard you will feel these muscles working. The A.M. are also responsible for keeping the airstream constant and also its pressure.

Many people do vibrato with their throat, without noticing it. It's a bad thing to do since you need it to be relaxed so the airstream keep going out freely.