"We have dogs."
Translation:On a des chiens.
Yeah, it's tricky. You almost always have to use an article in French. I always pick des if the number of the noun is not specified.
There's a discussion about this question: https://forum.duolingo.com/comment/3683850/Les-or-Des
Might just have to keep practicing until we get a feel for it. Sometimes that's the best way to learn a language, repetition of what's right until it feels right rather than learning all the rules.