In general, you do get tax relief on any pension contribution, which is why they are a good way to save for retirement.
This means that a £1 contribution will in effect cost a basic rate taxpayer 80p. If you are a higher rate taxpayer you may receive more tax relief.
Usually, you simply pay your contribution and your pension provider will claim your relief from the tax authorities.
You can find details of how HM Revenue & Customs deals with pensions tax issues here.