Tilt-turn is a product where the window has a built-in ventilation mode. It is easier to work than a standard inwards opening window since it does not require the installation of a friction stay to hold the sash in place during ventilation.
Turning the handle 90° enables the tilt mode where the sash is opened for ventilation. Turning the handle 180° straight up activates the cleaning mode where the sash opens inwards like a standard window.
Here is a short video clip showing how the handle works in the tilt-turn windows.