When talking about something specific, like a ring, for example, and saying that it belongs to someone, you could use the genitive. For example:
"Это кольцо моей сестры"
Great. My questions are
1- are there other ways of saying that, that sound more fluent?
In English you can say "this is my sister's" when referring to the ring, or "it's my sister's" and people would understand it's about the ring in context. Is it the same in russian? Could you say "это моей сестры" ?