If you're just using a mobile app then indeed you are missing a big part of the Duolingo experience.
Each skill (such as "Shapes", "Countries", "Possession", etc.). can have tips and notes, and (nearly?) all of the Welsh skills do have very useful ones. But they're only visible on the website.
See e.g. https://www.duolingo.com/skill/cy/Possession .
So I strongly recommend that before you start a new skill, you open that skill in a browser (your mobile phone's browser might do, though you may or may not have to tell it to pretend it's a desktop otherwise it might just open the app or show an app-like mobile view of the website rather than the full one with the tips and notes).
Yeah, I've often wondered why if Duolingo is so popular on mobile they don't provide the notes. They're pretty essential to someone who actually wants to learn a language (rather than just play a game). It baffles me why they've just released Japanese on iPhone - a language which is so different to English and needs a lot of explaining - but without a single note of explanation.
Though "at least" the iOS app doesn't have access to sentence discussions, so you don't get confused learners posting the same question over and over on three dozen different sentences that have already been explained in the notes.
The choice on Android to have sentence discussions but no notes feels particularly frustrating to me.
At the moment Duo does not provide the notes on the mobile apps, although they apparently hope to do so in the future. You have to use a web browser to get to the browser version of Duo to see the notes. They are formatted so that they are easy to read whether on a computer or on a mobile device.
Certainly on this course we would recommend that you do read the notes before beginning each new section. They usually give an explanation of the patterns being introduced and some examples, and sometimes supporting information and items of interest such as the four/five main dialects, some 'Britishisms' in the English translations, exceptional patterns, national holidays and so on.
The very first set of notes explain the background to the course, including the level and register of Welsh that we cover and some other general points to bear in mind.
I have all golds and was practising to keep it that way when I found Nature de-golded, so started the practice, I think I had only done the subject once! I did virtually all on my iPad and finally looked on my laptop to find discussion. great! But now, in trying to ask why 'the' Welsh Mountains, and, en route realising it was Cymru not Cymraeg, I find all this about notes! OK, never seen them, managed without them, but - would I gain anything from looking and how do I find them? I might need them if Welsh2 ever arrives! SORRY FOLKS! Found them by looking at beginning of subject on lap top!
You will find them if you use a computer web browser to access the course. For some reason Duo recently stopped them being available through web browsers on mobile devices without using a workaround. One workaround is to use the Puffin browser, apparently - https://www.duolingo.com/comment/17638579
This is explained in the notes for the section, which gives more examples. There is no need for y/yr in the Welsh pattern.
It is another case which underlines the fact the Welsh does not translate word for word into its English equivalent.
The nearest literal translation would be 'the mountains of Wales', but it is usually rendered into the more common English wording 'the Welsh mountains'.
There are a number of named mountain/hill areas in Wales.