You can see three unhappy people in front of you - Marcia, Charlie and Ondon. The objective of the game is to make happy as many people as possible. You can make them happy - even when it seems to be impossible - only by use of arrows (+CTRL/+SHIFT)! I recommend to read help (see the button Help below).
A concise explanation of the preferential curves is on the page: http://preferencialcurves.klimes.us