This is the service that is used to buy and sell Bitcoin. The price is determined by the supply and demand among customers. You can buy Bitcoin with Japanese yen or sell the Bitcoin you own in exchange for Japanese yen.
BitFlyer offers a platform for customers to buy and sell Bitcoin. BitFlyer provides two services for trading Bitcoin: bitFlyer Lightning (a Bitcoin exchange for professionals) and the Bitcoin Exchange (a simple exchange).
On the Bitcoin Exchange, bitFlyer is the other party in Bitcoin transactions. You can buy Bitcoin from bitFlyer and sell it to bitFlyer.