There are two ways of saying can in Welsh, using gallu (south) and medru (north). It’s best to be aware of both, and let local usage dictate which one you use. The only time medru wouldn’t be used is in the sense of permission, when cael would be used instead.
Do not use yn, and following verbnouns such as dysgu, to learn, will take soft mutation in the affirmative and interrogative, but do not mutate after dim. Medru is sometimes used with the affirmative particle mi which causes soft mutation.