Bitcoin is a decentralized digital currency, without a central bank or single administrator, that can be sent from user to user on the peer-to-peer bitcoin network without the need for intermediaries. Transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain.
Bitcoin is unique in that there are a finite number of them: 21 million.
Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services.
As of February 2015, over 100,000 merchants and vendors accepted bitcoin as payment.
To use bitcoin in the United States, you first need to acquire some. The most common way to do this is through an exchange such as Coinbase or Kraken.
These exchanges allow you to buy bitcoin with fiat currencies (like USD) and sell bitcoin for fiat currencies as well.
Once you have acquired some bitcoins, you can then use them to make purchases online or in person at businesses that accept bitcoin. You can also hold onto them as an investment, or trade them on cryptocurrency exchanges.