"My parents are bilingual, but I am not."
Translation:Tá mo thuismitheoirí dátheangach, ach nílimse.
Would someone explain to me why is this "nílimse" and not "nílim", and how do I know when to use the one over the other? Does it have something to do with "mo thuismitheoirí" denoting ownership?
The exercises are the lessons. There are Tips & Notes available for many of the Skills on the website that give some explanation of of the grammar of each topic, but you learn vocabulary by encountering it in the exercises, just as you learned vocabulary as a child, and you can get further explanation of various points by reading the comments on the exercises.
Well, tuismitheoir means parent, and that's the literal meaning of it. If you're looking for the etymology, wiktionary says that it comes from the Irish verb tuismigh, which means to beget or to produce, specifically as in offspring, and the suffix -eoir, which turns a word into an agent noun.