"Mis Mawrth a mis Ebrill."

Translation: March and April.

[terrimellor0]

why is "mis" there if not used? should I use mis before the month

[NicDafis]

It's usually best to do so, if only to keep things simple. Without mis in the example here, you'd have Mawrth ac Ebrill, for example, and using mis also avoids having to deal with things like yng Nghorffennaf and yn Nhachwedd. (If you haven't come across mutations yet, don't worry, it'll be fine! The course is good at introducing them in a gentle fashion.)