If you are referring to the size of the tiles, they are based on 8x8px. In case it wasn't that I would need more information about your question.
the grid mean to break tile to draw on unity or unreal using tilemap
In the 4 terrains you can make an autotile or terrain and simply draw the terrain. In the extra version they are already prepared with this function for godot.
By tomorrow I will update the page showing more details.
I hope I have solved your doubt.
thanks
Here you can see the different variants of terrain tiles and how they will work.
