The main purpose of National Insurance (NI) contributions from the individual's point of view is to qualify for a State Pension. That said, NI payments are not reserved by government as a resource to fund pensions, they just form part of the country's general receipts and pensions are paid out of the country's current account.
There are various classes of NI contributions and these are detailed on this gov.uk web page. The data for the following summary table was taken on 19th March 2016.
|National Insurance class||Who pays|
|Class 1||Employees earning more than £155 a week and under State Pension age - they’re automatically deducted by your employer|
|Class 1A or 1B||Employers pay these directly on their employee’s expenses or benefits|
|Class 2||Self-employed people - you don’t have to pay if you earn less than £5,965 a year (but you can choose to pay voluntary contributions)|
|Class 3||Voluntary contributions - you can pay them to fill or avoid gaps in your National Insurance record|
|Class 3A||Voluntary contribution - you may be able to top up your pension with a single lump sum if you’re due to retire before 6 April 2016|
|Class 4||Self-employed people earning profits over £8,060 a year|
You can get a statement of your NI contributions by following this link.