Touch the monitor to focus and lift your finger to take the photograph.

Touch Photography (Touch Shutter)

(Touch shutter/AF:On)
Touch the monitor to position the focus point and focus (autofocus only; the touch shutter can not be used to focus when the focus-mode selector is rotated to M to select manual focus). Focus locks while your finger remains on the monitor; to release the shutter, lift your finger from the screen.

(Touch AF: On)
As above, except that lifting your finger from the screen does not release the shutter. If subject tracking is active, you can focus on the current subject by tapping the monitor.

(Touch shutter/AF:Off)
Touch shutter and AF disabled.