Some people say that my puzzle designs often are too difficult for 'normal' people. So, this is a puzzle especially dedicated to persons getting into contact with puzzles for the first time. You easily can solve it while drinking coffee with your friends ...
It consists of only four pieces. Each piece is a flat wooden square having one pin and two holes (on opposite sides). All four pieces are different:

The (first) objective is to assemble the four pieces resulting in a square of 2x2 units, with all pins 'inside' e.g. no pin is visible at this moment:

But this is only one of four arrangements that are worked out using this set of pieces. Here are the other ones:

               

After you have successfully assembled all four patterns, you can scramble the pieces and start over from the beginning. Even if you have solved this puzzle once, it will be a new (small) challenge to solve it again.