If you're in doubt of a word's gender, you can always look it up online (like here by the side of bøjning), Den Danske Ordbog also gives plurals to help you recognise irregular plurals

Definite word can end in either -en (common gender) or -et (neuter gender).

kage (c) / kagen
kylling (c) / kyllingen
æble (n) / æblet

So yes, it does make things definite. It's just also a good way to see a word's gender, like attaching an article.

[2019/05/13]