"They go out after dinner."
Translation:Zij gaan uit na het avondeten.
Ah yes, the tricky thing there is that "rijst" and "kip" are not singular nouns in that sentence. They are uncountable. Just like you cannot say "one rice, two rices" in English (unless talking about different rice species, which is not the case here), the same is true in Dutch. As a type of meat (instead of an animal), "kip" is also uncountable.
Uncountable nouns, just like in English, do not get an indefinite article. So instead of saying "een rijst" (a rice) you simply use "rijst" without an article. You could still use "de rijst", but that would point to some specific rice and the meaning would be different.
I hope that clears things up a little bit.