I'm sorry for your struggle :(
I completed it from scratch along with the idea itself in 3 days, so didn't have enough time for a proper tutorial. Wanted the players to figure out their own as a form of puzzle.
The answer to the 5th level is "BRACKEYS". You don't have to finish it tho. It'll only bring you back to 2nd world. You can unlock platforms on the 2nd level by staying on the platforms from the 3rd level for just 2 seconds each. They're in the exact same place on 2nd level, just jump on them. In World 4, you have to use a door 3 times to complete a pattern, and the sequence of using doors matters say you used door 2 after 1, it has a different path.
BTW you can finish the game at the first level :>