Employers withhold part of your salary - I think it's a fixed percentage based on the height of the salary - and pay that to the tax authority.
Yearly, citizens file their taxes, giving information that the employer doesn't have or does not take into account (like gifts to charity, partner income, mortgage interest paid, health care related costs, tax paid on dividend, ...) that results in more or less taxes that should have been paid. After receiving that tax-related information, the DTA calculates what you should pay additionally, or whether you get some of the taxes paid back.
Yearly, citizens file their taxes, giving information that the employer doesn't have or does not take into account (like gifts to charity, partner income, mortgage interest paid, health care related costs, tax paid on dividend, ...) that results in more or less taxes that should have been paid. After receiving that tax-related information, the DTA calculates what you should pay additionally, or whether you get some of the taxes paid back.