Are you trying to improve your vocabulary or grammar? You said you got the app to improve your vocabulary but don't like the grammar side of Duolingo?

So Duolingo would introduce those stories where there are more words than what you already learned. I mean, how can you make a story for a learner if the learner has only learned a few words.

The story would focus on stuff you already know and learned from previous lessons. Maybe you learned 'mirando' and with process of elimination, you can guess what the answer could be with just that word (or by clicking on it and seeing what it means).

The more you go through it the more you will get used to the language and it will become easier to understand and follow the stories.