There's 4 Ghosts in the game:
-Blinky (Red)
-Inky (Blue)
-Pinky (Pink)
-Clyde (Orange)
And each maze has 4 Power Pellets, the big dots in certain corners of the mazes, i recommend walking around the maze until all the 4 ghosts get near you, then eat a Power Pellet and eat the 4 of them as fast as possible, you'll get an achievement afterwards.
Also, try to do the same process with the three remaining Power Pellets in the same maze to get a few more achievements.