Drawdown is effectively your choices built upon a pension. It gives you the opportunity to take an amount of money out of the pension without necessarily setting up a regular amount.
It is flexible means by which you can access your pension funds at any time with tax implications. It aims to replace some of the income that you would have got through work.
It is there to allow you to meet your financial means in the most tax efficient way possible. Advice is best sought before doing so.