Click any of the buttons on the faces of the puzzle to make a move. (Left-click and right-click move in opposite directions.) Click the upper-left corner to toggle an 'X-ray' view mode. Click and drag anywhere else to rotate the entire polyhedron to a different angle.
If you have difficulty telling colours apart, press 'C' to toggle text labels.
There are many different puzzle shapes to choose from. Some puzzle configurations include black facets, which don't need to be matched.
Full instructions | Simon Tatham's Portable Puzzle Collection | Source code