Slide the blocks around - they merge when the touch. It's simple once you try it.

Nice little puzzle game, though I’m not sure I’ll buy it as I think the Master challenges will give me nightmares.

(Apologies for brevity of my posts today, by the way, I’ve had a long, long day already and it’s barely even lunchtime. Had to get up two hours early to drive for an hour for a hospital appointment, then drive back, then get into work, etc.)