I am trying to buy bitcoin . i research online take some advise from people who are involve with it ..But to get exact point its bit uncertain ...so what should i need to know before buying bitcoin?
You should know what is private keys and that you have to keep those a secret, don't use online services like exchanges to store your bitcoin. Because with them you don't have ownership of your bitcoins, but you trust 3rd party with it. Go with good and reputable exchanges such as coinbase (gdax), gemini, kraken.
Don't belive any website that promise to get you easy and quick money, but investigate and if you have to ask about that service here. There are many scams and ponzi scemes which is why you want to make sure website is legit.