Bitcoin is one of the existing virtual currencies, but also the largest and safest (in terms of transaction volume). In any case, it is a decentralized and intangible currency, that is, it does not exist physically and does not depend on any institution. Who then exercises control? Own customers and programmers.
There are no intermediaries, transactions are direct between users. Each of them manages their bitcoins in a virtual wallet, and when they make a transaction, it is recorded in a public database: the blockchain.
But in addition, some of the users are responsible for verifying the transactions, to record them in the account book and to make sure the network works: it is the miners, programmers who take care of security in exchange for bitcoins.
It is a global currency, and any user is free to send any payment in any part of the world instantly. In addition, the commissions are low (no intermediary being necessary), the use of open source guarantees transparency, and because of its decentralization nobody can modify the system as it sees fit.
In addition, for companies, the use of this type of cryptocurrency gives much visibility, since it is placed on specialized sites that stand out worldwide, reaching new customers.
Similarly, these currencies are useful for companies operating in different countries, since with a single platform for payment and exchange of virtual currencies, they can reach any market.
To conclude in a few points: