S’mae posting this question for a friend who’s unfamiliar with the forum diolch.
I am learning Pwy biau’r car? Who own’s the car? sentences at the moment. The answers are Hugh biau’r car. Hugh owns the car, or Fi biau’r car. I own the car. When I put Dw i’n biau’r car. in google app it says that it means I own the car. So they both mean I own the car, but the Fi biau’r car, is a form used to answer the question and is a bit more emphatic than Dw i’n biau’r car. is that correct? Thanks for any answers.
Follow on from above, the app actually translates Dw i’n biau’r car as The car is mine which I’m assuming is the same as I own the car. Also I know the app gives an alternative way of saying to own, but working on making sure I’ve got the alternatives with Dw i’n biau’r car. Fi biau’r car. Also I’ve seen Pwy sy’n biau’r car as an alternative somewhere, presumably both are acceptable. Sorry this is question is so long. Diolch.
No, that is not quite correct. biau is not a verbnoun, so it doesn’t take the usual linking yn. And because of the identifying nature of sentences with biau, the word order is always that of emphatic sentences.
Pwy biau’r car? Fi biau’r car. – Who owns the car? I own the car.
I thought that Hugh owns the car. – O’n i’n meddwl taw Hugh biau’r car.
Diolch Hendrik
Is there a north/ south variation with this Diolch.
No, there isn’t.
Diolch yn fawr 
Added just for the benefit of anyone who might be trying to look it up in a dictionary: It’s actually piau (with a p), but because of the way that it’s grammatically used in sentences (as summed up by @Hendrik ) it almost always gets its initial sound softened from p to b.
Diolch Rob much appreciated
One lovely exception was seeing the Caerdydd/Cardiff signs on bike trails saying
“Pwyll piau hi” - Caution owns it (her) / Common sense owns it
Also the Welsh idiom
AMYNEDD PIAU HI - Patience wins the day (best English translation I can think)
A nice bit of alliteration there - perhaps it would help people remember? 
Twyll piau hi is an ironic joke version I’ve heard somewhere.
How do you think I can recall it? 