Bitcoin

When i made this book one btc is only 900 US Dollar , 3 months after is equals 2600.00 US Dollar , Today the poeple to hear me before is happy One Btc is near 5000 US Dollars again, and i dare to say it will end the year in 7000 US Dollars plus, today is near the end of 2017 and 1btc is 15000 US Dollars.

What is ?

How does it work?

And why should I buy at least some for the future?