Bitcoin, also known as BTC, is a digital currency released in 2009 by a group of men known as Satoshi Nakamato.
Bitcoins can be traded instantly* by anyone to anyone. The only requirement for using bitcoins is having an address to a wallet. You can acquire such an address through the softare provided by the bitcoin maintainer, other third party wallet software, or multiple online wallet services.
Bitcoins can be acquired through mining with your CPU or GPU (video card), or purchased from dealers and bitcoin exchanges.
The first thing you want to do in order to get into the bitcoin world is to get a wallet. This can be done using an online wallet service or by downloading the official client. The official client requires 8GB of hard disk space to start with, and that space will grow with time. The reason for this is that the block chain which holds all of the transactions is downloaded and stored locally. The block chain holds the required information for all transactions made on the network. You can use the block chain to verify that transactions are real, and to verify if payments have been sent or received.
The following links are the beginners essentials. You can download the official client from the site linked below: