Bitcoin is a decentralized peer-to-peer electronic cash system, secured using cryptography, allowing us to quickly and anonymously send value using the internet. It was introduced in October of 2008 by a person or a group of individuals named Satoshi Nakamoto. Bitcoin is open-sourced software and everybody can contribute to the project. You can send parts of a Bitcoin, up to 0.00000001 (called a Satoshi). To send and receive Bitcoins, you can use a web based, software or hardware wallet, each having different security characteristics. Each wallet has a receive address for each coin and a send section. An address is made up of letters and numbers (alphanumeric). Transactions are irreversible, unless the person agrees so send back the funds. If you wanted to send coins to someone, you would ask him for his receive address and paste it in your send section with the number of Bitcoins you want to send.
You couldn’t send digital currency in the past, since it was impossible to know if you sent the same funds to more than one person, that problem is called double-spending. The creator(s) of Bitcoin tackled the double-spending problem in two ways; everyone on the network can see every transaction and agree it is valid; and every transaction is connected to each other as a blockchain.