They both mean ‘to direct’. What’s the difference in terms of use?
cyfarwyddo is generally to direct in the sense of instruction - e.g. to direct a play, cyfarwyddo drama
cyfeirio is generally to direct in the sense of sending/movement - e.g. to direct an email to someone, cyfeirio ebost at rhywun.
I see that siaron has beaten me to it, but Cysgair says that “cyfarwyddo” is to: accustom, brief, familiarise, inform and instruct. Hence the sense of directing a play and the related plural noun “cyfarwyddiadau” / “instructions”.
“Cyfeirio” is to refer to (information) or refer a person to something, e.g. a specialist. It is also for addressing a letter or email.
Would cyfarwyddo be used in terms of a policeman directing traffic then?
Both could be in some senses, but I think the tendency with that would be to use rheoli instead.