Bashing the Bohrok
To do damage to a Bohrok or a Bohrok-Kal, you must get it to unroll. When you're battling a Bohrok or Bohrok-Kal as Toa Tahu (the red one)or Gali Nuva (the blue one), they will randomly unroll to attack you. If you're playing as Toa Kopaka (the silver one), then you must get close enough that the Bohrok is targeted. Then, use your shield This will unroll the Bohrok (attack it quickly and as many times as possible during the 3 seconds that you have before it rolls up again).

Bionacle of light takua nuva
Complete the game with all 6 toa including toa tahu nuva's quest to unlock the bionicle of light takua nuva

Extras
Collect all of the Lightstones with each Toa to unlock an item in the Extras menu