How does a propfan work?
To keep it simple (source for all that follows is Wikipedia - Propfan):

You can think of the contemporary propfan as a turboprop that has two high rpm contra-rotating propellers or fans with six or more highly swept fan blades each. These fans are driven by a turbine engine through a reduction gear or a low-speed free turbine.

High rpm is used to reach higher speeds and altitudes than conventional propellers.

The contra-rotating fan arrangement is used to remove torque effect, and to enhance efficiency (note: some early versions had just one fan).

Fan blades are swept to keep drag minimal at high rpm (high blade airspeed).

This description might very well be considered an oversimplification, but I guess this is what was asked for.