There's 4 Ghosts in the game, each has a different gimmick:
-Blinky (Red)
He chases Pac-Man and stays very close
-Inky (Blue)
He chases Pac-Man but stays further away
-Pinky (Pink)
She stays ahead of Pac-Man
-Clyde (Orange)
He just walks around without focusing too much on Pac-Man, he tries to chase Pac but gets scared and runs away
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.
For this achievement in particular, you need to eat all 4 ghosts two times, i don't remember if you're allowed to die, but if you are, only die when you're getting closer to eating 4 ghosts four times, because you only have 2 to 3 lives in the first stage so you can't just waste them.
Do this only during the first stage since it's the easiest and leave it for after you got all other progression achievements so you don't get distracted and lose focus on the later levels