Your goal is to fill all spaces with galaxies, but there are rules:
All galaxies have to keep their rotational symmetry, cannot be destroyed and there cannot be any overlap.
Drag a galaxy piece to a space to fill or to replace that space with the selected galaxy.
You'll notice that the galaxy will stay symmetrical, sometimes changing an other galaxy in the process as well if possible.
To remove a galaxy piece, you can either drag empty spaces onto it, or drag pieces of the same galaxy onto each other.
The centers of galaxies cannot be removed.
You cannot go over the edge of the board and another galaxy's center cannot be changed. If something does not work even though the space at the cursor is free, check at the galaxy's opposite end.
Finally, if you are confident a space is filled with the correct galaxy, you can click/tap and hold for a bit to lock it in place.
Clicking/tapping a locked piece will unlock it.
And that's it! Have fun!