Press the green flag to start. The first picture shows your aim. The blank spot can end up in the bottom left or bottom right. That means that the pure green tile can also end up on bottom left or bottom right. Hold space to mix them up. Click a tile next to the blank spot vertically or horizontally to move it there, thus creating a new blank.
The tiles are a bit overlapping. I don't know how to fix it. Based on a real life 3x3 puzzle. Ps: I'm a terrible drawer