The first sokoban game was created in 1982 by Hiroyuki Imabayashi at the Japanese company Thinking Rabbit, Inc. “Sokoban” is japanese for “warehouse keeper”. The idea is that you are a warehouse keeper trying to push crates to their proper locations in a warehouse.
The problem is that you cannot pull the crates or step over them. If you are not careful, some of the crates can get stuck in wrong places and/or block your way.
It can be rather difficult just to solve a level. But if you want to make it even harder, you can try to minimize the number of moves and/or pushes you use to solve the level.
To make the game more fun for small kids (below 10 years or so), some collections with easier levels are also included in KSokoban. These are marked (easy) in the level collection menu. Of course, these levels can be fun for adults too, for example if you don't want to expose yourself to too much mental strain.