Some of the income you earn is tax free, up to your personal allowance, each year. For most people their personal allowance is £11,000, which means you can earn up to £11,000 each year before paying any tax.
Your Personal Allowance may also be bigger if you get Blind Person’s Allowance an additional £2,290 (2016/17).
For anyone whose annual income is higher than £100,000, the personal allowance reduces by £1 for every £2 you earn over £100,000. So if you earn over £122,000 your personal allowance is reduced to nil.