Does it matter if you press the button halfway or instantly?

I own a typical 5mp canon digital camera. When taking a shot, does it
matter if you press the button halfway through before pressing it all
the way or should I press it all the way down in one quick motion? I
know it's a stupid question but I'm a newbie. The manual says when you
press the button halfway, it gives the camera time to focus and when
it's focused you press it all the way down.

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