that is what the website asks for. The reality is that you have to produce it in spades. If you can't produce extensive bank statements, a job contract, a housing contract, serious covering letter explaining exactly why you are visiting, what you are doing, who you know there, your full travel history, your life in the home country and why you are coming back, you ain't getting a visa.
I have friends resident in the UK, housed in stable housing and working who were refused a Schengen visa to go visit family in Norway. They had not given sufficient detail. The UK is worse