Greetings. Now first of I want to say that the third eye is a chakra, not a literal eye like some people think. So if or when you open it you won't physically change if you get what I mean :) Now, the third eye represents psychicness and being open and aware of higher or different energys we wouldn't acknowlage on everyday life. So opening the third eye supposedly "raises" your psychic abilities alowing you to see/hear/sense spirits, "predict the future" and more. If I was you I would be careful with opening this as it can allow you too see things you may not want to see, and it can be a bit scary if your not prepared. Like all things, I think it's better to leave your chakras alone and let them develop in their own pace, but of you really want to open it then I suggest doing meditations, or binrual beats. There are many other ways too, research it ;) I hope I helped! This took me a while to write.
Have a lovely day. - Rowan