The way you balance air flow and the muscular pressure in your larynx affects how your vocal cords vibrate. If those two things are unbalanced, then you can get
phonation that is either breathy or pressed. How we start a note is called a "
vocal onset," and these can also be breathy or hard. In general, we want to maintain the habit of balanced phonation and balanced onsets, with breathy and pressed/hard options saved for emotional effect.
You may have heard about "
vocal fry," which is a common way that people use their voices in the media nowadays, with low muscular pressure and low air flow, so you get a creaky sound. As a singer, it's not great for your vocal cords, and results from inconsistent air flow, so it's a habit that doesn't demonstrate good breath control.