Bitcoin is a virtual money (or better cryptomoney) based on P2P. For their features is used especially by hackers or who develop and deploy ramsonware, but not only.
How Bitcoin works? A good starting point can be the FAQ on official site.
You can buy Bitcoin using various services (read below), even with Ebay or collect with mining process.
If you want to become a miner, over a dedicated hardware, you need specific software.
To use Bitcoin you must have a wallet that allows start making payments with merchants and users.
How can you use Bitcoin?
A Reddit user has asked members of the Bitcoin subreddit how they spend their bitcoins on an everyday basis. From Food Delivery to Electronics, from Gaming to Gift Cards, etc…
Due to increasing popularity there are various Bitcoin services, here a list of the most useful:
Coinmill is a currency converter, from BTC to USD/EUR etc… and viceversa
Gobitcoin.io is another currency converter
Snapcard and Coinbase are two popular wallets, they allows to easily buy and sells Bitcoin.
LocalBitcoins allows to easily buy and sell Bitcoin.
Coinmap is a global map of Bitcoin accepting venues.
Bitpay is a trusted payment platform