وَنَجَّيْنَـٰهُمَا (And We saved both of them) is a past tense verb — the action already happened and is complete.

We translate it in past tense — "did", "created", "said", etc.

وَنَجَّيْنَـٰهُمَا (And We saved both of them) uses form II (فَعَّلَ) — the middle letter is doubled, which makes the meaning stronger or causative.

The meaning is more intense than the basic form, or means "to make someone do [action]".

وَنَجَّيْنَـٰهُمَا (And We saved both of them) starts with وَ, the most common Arabic word — it means "and".

We add "and" to connect this to what came before.