1. To show character development
2. To provide information
3. To advance the plot.
Hopefully, the Opening Scene should fulfill one of these purposes. In this scene, you are introducing a character and showing a bit of what they are like. This scene can be just one of the main characters or more than one can be shown but focus on one character. Here, is where you can introduce what kind of plot the story will follow. and give a bit here about the what and why. If you can manage it you need to provide information like when and where the story is taking place.
I looked at some of my own stories and saw how different the openings can be. In one, a medical suspense, the shadow character opens the story. There is no name given nor a description but through his thoughts you learn a lot. This scene also establishes one of the important places of action, the hospital and also the reader learns a bit about the plot. The kind of story is established.
Other openings can be a meeting between the hero and heroine or the villain and one of the main characters. You can establish the hero or the heroine and give lots of hints about what the story is to become.
Also the opening scene needs to give the reader the type of story it will be. Is it a mystery, a suspense, a romance, a fantasy or science fiction story. I judge contests and what I find is often the beginning writer will have a great first line but then nothing happens or they head into the backstory without moving the story forward. Often the information given could come in later during a conversation or some other mention. Often it is something the writer needs to know and not the reader.
So when you're starting a story, remember the three things a scene can do. If you achieve one, good, two, great and three fabulous. Keep the tome of the story to the genre you're writing. There's nothing worse than thinking you're going to be reading a comedy and find it turns into a tragedy partway through the book.