Learning about your head voice is sort of an advanced topic. It's definitely not a basic singing exercise.
It's probably not something beginners need to deal with, however if you're familiar with it and want to improve your voice in every way, then consider this explanation from Aaron.
Aaron is the #1 singing coach out there right now, and is programs have literally helped thousands of people sing better.
Head voice is basically a resonator, similar to your chest voice.
Chest voices is deeper and creates a fuller sound. Head voice is slightly lighter and creates a higher.
So how do you find this head voice? Watch the video above, and then the second one below.