Can someone explain mutations for me?
I've lived in Wales most my life but have never understood mutations, I only know there are 3 types but never when to use them, can someone help?
There are many reasons for mutations, far too many to sum up in an answer here. Only some of them are covered in this introductory course. As new reasons for a particular mutation are introduced in the course for the first time they are explained in the course notes for the relevant section - https://forum.duolingo.com/topic/924/hot and see the sticky discussion on 'Course tips and notes'.
This free downloadable guide to basic Welsh grammar has sections introducing some of the common reasons for the mutations - https://www.bbc.co.uk/wales/learnwelsh/pdf/welshgrammar_allrules.pdf
Whilst it is good to learn mutations .. it is certainly NOT the best idea to concentrate too much time on them when you are at an early stage of learning. Just absorb the mutation rules applicable to the section of work you are learning .. practice them .. it will all come naturally in due course :)