Here we are given ble as the Welsh for the interrogative 'where'; in another part of this section the same English pronoun is rendered in Welsh as lle. What, if any, is the distinction between these two forms? Is it a matter of regional dialect? I cannot remember any reference to this in the course notes.
"Ble?" always means "Where?" where as "Lle" can mean "Where?" or "Place". I'm not personally aware of any dialect preferances and here both used, so just chose which one you prefer and remember that "Lle" has the two meanings where as "Ble" has just the one.
Where are these course notes that people keep refering to? Can't find them!
They're not in the apps (one reason why I personally would not recommend them for learning but only for revising), but on the website.
When you open a skill and before starting to learn it, there are tips and notes for most skills written at the bottom. For example, https://www.duolingo.com/skill/cy/Days talks about the days of the week and how to talk about morning, afternoon, evening, and night.
Though even on a mobile device, it should be possible to open them if you use the mobile browser to access the website. (Some report that you have to switch the browser to pretend it's a desktop otherwise it may be shown a mobile view which looks a lot like the app and does not include tips and notes.)