ilomilo consists of 4 chapters each containing 9 levels and 3 bonus levels.
The aim of the game is to reunite ilo and milo.
There are 4 collectables in the game- safkas (little creatures that follow you when found), memory pieces, photos and records.
To proceed to the next chapter you are required to complete 6 levels by reuniting ilo and milo. you do not need to pick up collectables to gain access to the next chapter, do this until you've completed 6 levels in chapter 4 and the last level Platform 2 will unlock.
In platform 2 you have to get ilo and milo onto the train, not too difficult. When you have reunited them on the train the achievement will pop and the credits will roll.
This means you can get this achievement by finishing as few as 25 of the games 49 levels, without collecting anything.
If you are struggling on a level check the show hint option out in the pause menu. This game does get frustrating especially late at night. If you get really stuck put the controller down and go back to it the next day with hopefully a fresh view of it.
Good luck and have fun, leave feedback if you vote negative
EDIT-- for anyone struggling with the pronunciation it's definitely pronounced ilomilo