Bitcoin is the longest running and most trusted blockchain and cryptocurrency. It was the first decentralised digital currency with no issuing authority. It utilises a peer-to-peer network with transactions making heavy use of cryptography.
Accounts on the network use an asymmetric cryptographic Private & Public key system. Anyone can create a unique address using basic software on most computers. You can share this public address with anyone and control of the funds is possible with the private key.
As well as being the name of the network, bitcoin is also the name of the unit of account. Bitcoins are divisible to 8 decimal places, so 1.00000000 is one bitcoin. The smallest unit available is a Satoshi (0.00000001). New bitcoins get introduced to the network by a process known as mining.
Mining uses the computing power of users around the globe to validate transactions. This is an opt-in process that often uses specialised hardware and software. All mining users compete to confirm blocks of transactions with a specific algorithm. Whoever completes this challenge fastest locks in the previous round of transactions. They are also given some bitcoin generated by the network for their efforts.
The actual authors of the original Bitcoin software are still unknown. The Bitcoin project launched in 2009 under the pseudonym of “Satoshi Nakamoto”. You can view the original Bitcoin white paper here for a technical and economic introduction. It is open source software and has since benefited from voluntary development.