Pension Credit is an income-related benefit for those who have reached the qualifying age (in line with the State Pension age for women, which is increasing to 65, and the further increase to 66 for men and women by October 2020). It is made up of two different parts: Guarantee Credit and Savings Credit. To qualify for Guarantee Credit you must live in Great Britain.
The Guarantee Credit works by topping up your weekly income to a minimum level. In 2017-18, that level was set at £159.35 for single people and £243.25 for couples. You can check current rates on the GOV.UK web site.
Savings Credit provides additional help to pensioners who have a small amount of pension from an occupational or personal pension. The Savings Credit element of Pension Credit came to an end for most people who reached their State Pension age on or after 6 April 2016.
You can find out more about Pension Credit and how to apply for it on the GOV.UK website.