Every year, they add some improvements to the entire system. They basically prefill your entire income and capital. Including stocks, dividends and other things. The only things you need to fill in yourself are some of your deductions (there are some which are prefilled as well).
They open the filing of taxes every year on march first. And every year there are lots of people who fill it in on the first day. This year there was even someone who handed their taxes in 18 seconds past midnight.