This is a very simple achievement. You just have to beat the 4 different puzzles that are in the easy category.
These 4 puzzles are:
Tip: If you are not familiar with how this game work (like me) then when you are playing the puzzle you can use the help button (in-game) which shows you the pairs you need to match up. To access it you must enter a puzzle and tap the side of your screen. This will bring up a couple of options. The hint button is the light bulb. I found out that this can be very useful and best of all does not affect achievements!