Bitcoin is a general purpose digital currency. It is programmable money.
Nothing like Bitcoin has ever existed before.
In a similar way that email revolutionised the postal service, Bitcoin can revolutionise financial services.
With Bitcoin an international remittance is as easy as sending an email.
Regardless, it now being used by millions of people all over the world to conduct transactions. These people are the Bitcoin community. By reading this you are part of that community.
Bitcoin uses cryptography to prove to others that you, and only you, have the right to spend the funds under your control.
All of the cryptography in Bitcoin is well-known and used in countless other applications including banking systems. There is nothing new or special.
In short, if you trust mathematics, you can trust Bitcoin.
Obviously, you can receive bitcoins from anyone as well – perhaps as part of a crowdfunded project or a loyal fanbase.
Also, if you did find yourself actually typing one and made a mistake the wallet software will tell you that it is not valid.
Many Bitcoin wallets are “open source” which means that developers can look at how they work and verify that there is nothing suspicious going on.
It is not a requirement of Bitcoin that you reveal your identity. In fact one of the prime goals of Bitcoin is to avoid revealing your identity to anyone, but still allow you to conduct a transaction.
It is very like cash in that sense.
Overall, its anonymity is much closer to cash than to a credit card.
At present the block chain is about 65GB and growing every 10 minutes.
The fundamental problem was trusting the central checker. What if it was cracked and all the transactions rewritten? What if the central checker itself wanted to fake a crack in order to cover something up?
The task facing a Bitcoin miner is to fiddle with some settings for the block, without altering the integrity of the transactions, until that number is below a given target.
The lower the target, the greater the difficulty.
For the technically minded, a Bitcoin miner has to find a SHA256 hash that is under the target value.