In reply to emphatic questions (i.e. where the verb is not first so you don't use the verb). E.g:
James ydy dy enw di? Ie
Is this a word a beginner could use to mean yes, if you don't know the correct way to say yes? I still can't get my head around there being no word for yes! :)
Not as simple as that sorry. ie/nage are used to answer emphatic sentences. An emphatic sentence does not start with the verb (like I said above).
If you want a cheat way to answer yes without finding the correct word for yes, try answering with other words that indicate the affirmative like "OK / o'r gorau", "siwr" or "iawn".