autofocus – Half press on Nikon D90 triggers shooting

I’m starting to learn photography and, in one of the videos I watched, the guy said that its good to first half press the shooting button (on auto focus settings and P mode) and then full press to get the photo. But, in my D90, when I half press the button, it automatically shoots when it finds focus. How can I disable it, so I can find focus with half press, correct the photo and then full press to take the photo?

All settings are default, except Autofocus -> a1 -> Single point