If you are confused about the difference between tax and National Insurance, then take a look at the following:
Income Tax is a tax that you pay directly from your salary when your income goes over your personal allowance amount. There are some allowances that you may be able to claim to increase your personal allowance, and these include allowances such as Marriage Allowance and Blind Person’s Allowance.
National Insurance contributions are payable by all earners that are over 16 and who earn £183 a week or more. If you are self-employed, then you are liable to pay National Insurance if you have a total profit of £6475 a year or more. There are a number of different NI classes, and the amount you pay will be dependent on your personal circumstances.