"The milk is behind the cheese."
Translation:De melk is achter de kaas.
No, the combination 'zitten achter' can not be translated to 'is behind'. Your sentence therefore literally translates as 'the milk is sitting behind the cheese'. You could however say 'de melk zit in de kaas' > 'the milk is in the cheese'. So, 'zitten achter' > 'is behind' > incorrect. 'Zitten in' > 'is in' > correct.
Unfortunately, there is no way to know. You have to just remember which one fits for every word. It's a similar situatiion with many languages. Having said that, words that end in "je", such as het meisje are always het words.
The Welkelidwoord website has exercise that can help. The site also offers a daily email with the link to the exercise of the day (oefening van de dag). It's pretty useful. Here's a link: https://www.welklidwoord.nl/woord