Place coloured cube in empty grid, when there has same color nearby, they will be merged, you goal is to meet the targets in limited “moves”. 
Every round, you have there different cube set, becareful to pick one and drag to a better grid, of course you could make it more strategic, a chained-merging could allows you to clear a brunch of cubes vastly. The control is easy, instnivtily, just simple tap on wanted cubes and drag up to the grids.
There has some variety of the game, while some grids are locked, unlock when some conditions met.
Break the Tower, that absorbs merging cube, beat them first.
Cannon that shoots random cubes and place in random grids, it is maybe good that helping you merging, but this would also a bad that filling up all the places and make you game over.
Booster like rocket could allows you to clear one whole stack of cubes, make more empty place.
Windmill is a strong blower that instantly shuffle all the positions of cube, that is an important life-saver!
robot arm allows you to pick any stack of cubes and place to anywhere you want.