That looks almost like a tautology.
If I'm looking at a sunset, the reality is when the idea of looking at a sunset matches the reality of looking at a sunset?
Close but not quite. Truth is when someone's idea (possibly yours) that you are looking at a sunset matches the reality of you actually looking at a sunset.
If I have a specific experience, how do I tell that it's actual reality?
There's a couple of ways. One is post mortem. If you are in a shopping mall and you suddenly have an increadible earth-shattering godly experience, but nobody else and no security cameras share the experience then the content of the experience isn't actual reality.
Another way is to analyze the experience while it's happening. Mind generated experiences tend to have subtle flaws. For example, if you see a bright glowing super sized rose in front of you, look at the walls and objects in the environment. Is the light being reflected correctly or at all? Is a shadow produced when objects are placed before the rose?
The best answer I can give you is what we currently know about it. It is a presence of information that is consistent, persistent, and non-contradictory.
Can I really "actually" see anything, or hear anything? Can you?
Of course, your pediatrician tested you for these items as you grew up.
Can you prove that what you see or hear is actual reality? How would you prove it?
You can only prove things in mathematics where all variables are known and accounted for. You can however, show evidence that what you see or hear matches actual reality. Pictures, video recordings, and audio recordings are great tools to use if you are having difficulty in this area.
Do you need to prove to anyone except yourself that you can see and hear?
Sometimes.
Have you ever told anyone else about something you saw, and did they believe you, or couldn't you really "actually" tell? Did it matter to you if they believed your story?
I work with someone whom has exhibited a trend of forgetting certain details of what we talk about. I took note of the type of details that were frequently forgotten so one time when I saw discussion about the detail coming up, I hit the play button on a concealed audio recorder. Later, as expected, the person in question forgot the details and didn't believe me when I stated what he had said. So I whipped out the audio recorder and he said something like "holy shit, I really did say that!".