Tax credits including Child Tax Credit and Working Tax Credit are the payments from UK government. In the UK, if you have children or work on a low income, you may be able to claim tax credits. There are questionnaire on the HM Revenue & Customs site to give you a rough idea if you are qualified for tax credits. However, you can only know for sure if you are qualified after making a claim.
If you are likely to be qualified after completing the questionnaire, you can use Tax credits calculator to find out how much you can get.