[Nagareboshi]

When 二 is by itself, it's pronounced "ni". In this example　二時　(niji-2 o'clock) the pronunciation is "ni". The second reading is pronounced "futa". When 二 is paired with the hiragana　つ, it's pronounced "futatsu" 二つ. "Futatsu" is a counter for items.

I hope that helped.