Big Sister, Elder Sister
The kanji and the word are exactly the same. That means they share meanings as well. This is your older sister, by the way. Not somebody else's.
Since this word is made up of a single kanji, it should use the kun'yomi reading. You haven't learned this reading yet, so here's a mnemonic to help you remember:
Picture your older sister (even if you don't have one), her birthday is coming up and there's only one thing she wants from you. A necklace (あね). She's wanted a necklace for years and you're finally going to give her one. She'll be so happy.
My sister is in Singapore.
My sister's dad and my dad are the same person.
I have two sisters and a brother, so we are siblings of four.