"I don't like March."
Translation:Dw i ddim yn hoffi mis Mawrth.
This is explained in the notes for the section.
yn/'n is used to link between the verb-form of 'to be' - here it is dw i (I am) - and the verb-noun for the action involved - here it is hoffi (liking, to like).
In these patterns yn/'n is not translated, but it indicates that the verb is 'unfinished' - 'I like/am liking' rather than 'I have liked'.
(yn/'n has other uses which are covered later in the course. )