You can place the broken matchstick with head on any of the open places as long as it does not form a row (horizontal, vertical or diagonal).
Below is one example: Place your broken matchstick in the middle top row as shown above. The other player can now only play position 3. (1 or 2 would make him/her a loser). Thereafter your move could be 1 or 2.
The matchsticks cover an area of 3 square matchsticks. Unfortunately 2 of the matchsticks have not been used. Move 4 matchsticks to still cover an area of 3 square matchsticks, but now all the matchsticks must be used.