What is the significance of an apostrophe?

An apostrophe can signify possession of one or many things, it can be a contraction, it can be a quote inside a quote, or simply a quote.

Possession - Example: Ruth's bike was stolen. ^ The bike was Ruth's, and we know that because there is an apostrophe.

Example: The animals' food was destroyed by humans. ^ There are multiple animals, and they all have food. So, it signifies that there are multiple animals that have food.

Contraction - Example: You're getting on my nerves. ^ The word "you're" signifies the word "You are."

Quote inside a quote - Jim said, "The other day, someone said, 'I like Jake.'" ^ As you can see, if there is a quote inside a quote, then you use an apostrophe. In British English, you would just use an apostrophe instead of a quote

Example: Jake said, 'I really like you.'