It probably has been mentioned on another comment, I just haven't seen it yet. But when do you use Dw i'n' and when do you use 'Dw i'. Diolch!
This is introduced in the notes for the earlier section 'Present Tense 1'.
Dw i just means 'I am'. yn/'n is needed to link that to verb-nouns such as gwisgo, hoffi, etc and to adjectives such as oer, twym, etc. Yn has three main uses - see this