Hi, I am not sure if this has already been asked but are we suppose to sing with our mouth or nose ? do we just use one or the other? 

Also does anyone have tips on how to not keep the nose from flaring while singing?  

Thanks! 

Hi, Grace! Singing utilizes both mouth and nasal resonance.

And as for nose flaring, I'd actually say that's okay (depending on the tone and style you're going for). Many classical singers flare their nostrils at times to help open up more resonant space (and lift their soft palate).