What does "o'" mean? What's the main function of apostrophe in this type of context?

Native speaker’s answer
Rebecca
Here, <o'> is a contraction of "of." This is because it's written according to how the speaker says it! The apostrophe fills in for the omitted letter "f." Ex: I haven't seen that before. => "haven't" is a contraction of "have not." Ex: After hiking for a couple o' hours, I was exhausted.