From Duolingo:

To have, to own

• Mae car gyda fi. – I have/own a car (lit. “There is a car with me.”)
• Mae cath gyda Sioned. – Sioned has a cat.
• Mae pannas gydag Owen. – Owen has some parsnips.
• Mae cath gan Sioned. – Sioned has a cat.
• Mae gen i gar. – I own a car.
• Mae gan Sioned gath. – Sioned has a cat.
• Mae gynno fo bannas. – He has some parsnips.
• Mae gynno fo gar. / Mae car gyda fe. – He has a car.
• gen i – with me
• gen ti – with you
• ganddo/gynno fe/fo – with him
• ganddi/gynni hi – with her
• gynnon ni – with us
• gynnoch chi – with you
• gynnon nhw – with them