Lets clear this from below points.

Is bitcoin currency? - Yes,its is a new digital currency.

which country's currency? - It's not any country's currency.

who is the founder of bitcoin? - satoshi nakamoto is a founder of bitcoin.

In which year bitcoin found? - In 2009

why bitcoin? - using its easy and cheap.no middle men is here in bit coin transactions. And bitcoin not join with any country. so any extra fees in transactions.

what is the price of bitcoin? - in may 17,2017 its price is 1760.44 USD for 1 bitcoin.

 Is bitcoin transaction safe?why? - Yes,Its 100% safe. No one can hack this transaction. because its is 3 computer verification process.

 where to store our bitcoin? - In bitcoin wallet. It is blockchain

Is i buy a bitcoin as investment? - yes, sure. Now a day its is a best trending currency.

How to buy this bitcoin? - using coinbase application or for india using zebpay application.

 which platform i used when i withdrew mu bitcoin as USD? - you can use paypal or any similar platform.

so hope you understand,what is bitcoin and how it work.