Does this particular way of saying "Yes" always correspond to the english "I do?"
Often, it would correspond to "I am", e.g. Wyt ti'n canu? Ydw. "Are you singing? Yes [I am]." You wouldn't say "I do" there.
But that's basically it, yes -- you're replying with the appropriate verb form of bod "to be".
"Are we singing? You are (= yes). Are you playing? We are (= yes). Are you happy? I am (= yes). Am I pretty? You are (= yes). Is he jumping? He is (= yes)."
Dyn ni'n canu? Ydych. Dych chi'n chwarae? Ydyn. Wyt ti'n hapus? Ydw. Ydw i'n ddel? Wyt. Ydy e'n neidio? Ydy.
And the same for no:
"Are we singing? You are not (= no). Are you playing? We are not (= no). Are you happy? I am not (= no). Am I pretty? You are not (= no). Is he jumping? He is not (= no)."
Dyn ni'n canu? Nac ydych. Dych chi'n chwarae? Nac ydyn. Wyt ti'n hapus? Nac ydw. Ydw i'n ddel? Nac wyt. Ydy e'n neidio? Nac ydy.
The definite article is one of
depending on the sounds at the end of the previous word and the beginning of the next one:
- 'r after a vowel
- otherwise yr if the next word begins with a vowel
- otherwise y
There is no indefinite article.
So they're pretty easy to tell apart :)
There are several straightforward ways of typing accented characters, depending on your device and its operating system. There is an outline some common methods in the very first set of course notes - see https://www.duolingo.com/skill/cy/greet1/tips-and-notes.
It is better to find out how to type them directly rather than relying on Duo's incomplete character menu or cut-and-paste.
Accents can change both the meaning and the pronunciation of words.