Story.
(Certainly not the most important aspect in a puzzle game!)
As a soldier serving somewhere in the Middle East, you have to close all the platforms on each level. Starting on the Entry Platform and jumping towards the Exit Platform you have to close the others.
There is a time limit given to every level (see the counter in the bottom left-hand corner) – if the time is out, the level cannot be completed. Also note that you cannot fall too far or you will die. Fortunately, you have unlimited lives so you may start over and over again.
The game state (a list of unlocked levels) is saved automatically after you reach an unexplored level.
Platforms.
Starting on the ENTRY platform you have to close all the other platforms before reaching the EXIT platform. REGULAR platforms slide shut as you step off them. But many of the platforms have special powers: for example the Horizontal Shutter platform can close all the platforms in the same row and the Bounce platforms can fire our hero in some direction.
If all the platforms have shut before you reach the exit within a given time limit, you will be promoted to the next level.