〜必要がある
need to, it's necessary to
Verb dictionary form + 必要がある / 必要はない
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必要 means "necessity". After a dictionary-form verb, 必要がある says something needs doing: ビザを取る必要があります, "you need to get a visa".
It's more neutral and objective than なければならない, and you'll see it in instructions, notices and explanations.
The negative usually takes は: 必要はない, "there's no need": 急ぐ必要はない, "there's no need to hurry". It's a gentle way to say "you don't have to", like なくてもいい.
With nouns, 必要 works as a な-adjective with が in front: パスポートが必要です, "you need a passport"; 準備が必要だ, "preparation is needed".
Examples
日本で働くには、ビザを取る必要があります。
To work in Japan, you need to get a visa.
時間はたくさんあるから、急ぐ必要はない。
There's plenty of time, so there's no need to hurry.
申し込む前に、書類を読む必要があります。
You need to read the documents before applying.
明日は来る必要はありません。
There's no need to come tomorrow.
もう一度確認する必要がある。
We need to check it once more.