"I drink beer."
Translation:Dw i'n yfed cwrw.
Cwrw is the base word and mutates in some situations. Cwrw (because it begins with a C) mutates to gwrw (soft mutation) and nghwrw (nasal mutation) and chwrw (aspirate mutation). Two main instance come to mind as to when cwrw might mutate. Firstly it will mutate softly after dy and ei(when it means his). I.e dy/ei gwrw (your[informal]/his beer.). The other possessives that will cause cwrw to mutate are fy(my) which causes a nasal mutation (fy nghwrw) and ei(when it means her) which causes an aspirate mutation (ei chwrw). Finally it would softly mutate if it comes after one of twelve prepositions but the only one I could see being used would be "mae o'n gofyn am gwrw" which is "He is asking for a beer" where the "am" causes a soft mutation.