What it means
必要がある means that something is necessary or required. It is commonly used with a dictionary-form verb to say that an action needs to be done, and with a noun followed by の to say that something is needed. This pattern often presents necessity objectively and can sound more formal or written than 必要です. The polite counterpart is 必要があります.
Usage note
必要がある is different from なくてはいけない or なければならない. The latter expressions directly mean that someone must do something, while 必要がある states that there is a need for an action or thing.
How to use it
この会議には通訳の必要があります。
There is a need for an interpreter at this meeting.
申請書を提出する必要があります。
It is necessary to submit the application form.
この会議には通訳の必要がある。
There is a need for an interpreter at this meeting.
申請書を提出する必要がある。
It is necessary to submit the application form.