Does nuair translate only as "when", or could it also mean "while"?
I think "when" can have a few interpretations, one being that it happens at that very moment, and another that there is a small window of time between both actions--for instance, "We go drinking when we work", could mean that they drink on such days that they work, though this can happen afterwards and not necessarily while working.
On the other hand, "while" is used only as meaning at that very moment. So I was wondering whether the word "nuair" makes that distinction.
Duolingo might be okay for learning vocabulary, but it's really not very good for learning grammar. You might want to look at DCU's Irish classes on FutureLearn (www.futurelearn.com). They're free, have lots of audio, don't have the errors Duolingo does, and have live support.
In any case, you should get a grammar book so you don't need to rely on Duolingo. Take a look at Irish Grammar You Really Need to Know (https://www.amazon.com/Irish-Grammar-Really-Need-Know-ebook/dp/B00GU2MPVE) It's not a book for teaching yourself Irish but a reference book for looking up things you have questions about -- probably why the person who gave it a bad review was disappointed.
I know, that's why it takes me ages to read and try to figure things out and write and practice. I took Irish 101 on futurelearn, loved it, I'm waiting for the next one to start but that's gon be October. I do want to get a grammar book but the shipping to my country is way too expensive (more than the books themselves) and there are complications with the customs house here, that's why I haven't yet. I hope to do so when I get to travel back to Ireland. Thank you so mch for all your suggestions, I really appreciate that :)
Yes, I'm using that online grammar source (I studied german for 6 years but I haven't practiced for quite some time, years indeed). It's true that sometimes it's too much information and I lose myself, so I'm trying to focus on the basics to understand something and then move from there. Go raibh maith agat!
Are the two "they"s in "They drink when they run" different people or the same?
The first siad is the first "they", the second siad is the second "they". There is nothing in the grammar of Irish or English that tells you explicitly that it's the same "they" in both cases, though it would be natural to assume that they are, without additional evidence to the contrary. You could use an emphatic suffix in Irish if you wanted to imply that they were different groups.