You can obtain icon items by shooting at Chozo statues. Select an icon item with and use it when needed.

Missiles	Fire Missiles with .
Super Missiles	Fire a powerful Super Missile with .
Power Bomb	Press in Morphing Ball mode to set a powerful bomb. All enemies on-screen will take damage.
Grappling Beam	Fire this beam at special blocks with to lock-on with your grappling beam.
X-Ray Scope	Press and hold to reveal the location of hidden corridors and other secrets.