"Dw i'n mynd am dro."
Translation:I'm going for a walk.
My Welsh friend said 'Cerdded means to walk, or walking, and so cannot be used in the phrase 'Dw i'n mynd am dro' because cerdded can't mean a walk'. He's first language Welsh, however, so he has never really tried to grasp the grammar of Welsh; it's like how we know English- it's hard to explain the English grammar in another language.
Cerdded is the act of walking whereas "mynd am dro" is more akin to the English "going for a stroll" or more literally "taking a turn" (a phrase that has mostly fallen out of use in English - e.g. taking a turn round the park).
So if I was walking as a means of transport - dw i'm cerdded i'r dafarn - then cerdded, but if I'm taking the dog out where the purpose is the walk - dw i'n mynd a^'r ci am dro - then am dro
(a^ = a with a circumflex - to bach sorry, I can't work out how to type it properly, the MS shortcuts don't work and as my laptop doesn't have a separate numpad, I can't use Alt-codes)
When learning a new language, I find I learn much about English too - and my assumptions about ways of thinking are challenged. All languages have words which have several meanings, usually shades of the base meaning. However, the range of shades is never the same from one language to another and part of the fun in learning a new language is coming to understand how different peoples think about, for example, something as simple as walking...