All employees pay National Insurance contributions and if you do want to work then you must apply for a National Insurance number. The National Insurance Number (NINO) is a number unique to you to which will help your employer to pay your National Insurance contributions. No one else can use this number.
You do not need a National Insurance number to start work but you will need to get one once you have started a job. Your employer will give you a temporary number while you wait for your permanent number.
You can apply for your National Insurance (NINO) online in the Government website