A bitcoin is a type of currency, that is generated on computers and retained only in electronic form. It's decentralized and nobody prints it like US dollars or euros. Bitcoin is generated with people, who launch special software on own computers, this software is called "miner". Bitcoin is a 1st digital currency, well-known as cryptocurrency. The link below shows you a video, it's about bitcoin in general terms:
You may use bitcoins for payment in same way like US dollars, when you purchase something in internet. But bitcoins has a difference, because it's a decentralized as mentioned. It's important for some people, because centralization means a security, but nobody controls bitcoins like banks or somebody else.
As a code, it's developed with Satoshi Nakamoto. He offers to use this payment system, which is based on mathematical tasks solving. The main purpose is a decentralized currency production, some kind of electronic exchange in network but with minimal fee.
There is no person, who prints it as real money or mint coins, unlike of banks, who can do this officially with real currency, when it's important to pay off a debt.
A bitcoin protocol is allow to generate only 21 millions of coins. But bitcoins are can be separated on small parts, a smallest is a coin divided by 100 000 000, it's called "satoshi".
Bitcoin is created digitally, so anybody can be a part of community and become a miner, using a special software with own computer. This community(network) supports a bitcoins exchange, to make it a real payment system.
A basis of real money is a gold, silver, oil or any natural resource. In other words, if you have a dollar, you may get some oil, but banks cannot give you this, of course. But bitcoins basis is a mathematical calculating. Many people around the globe are using software, which is produced bitcoins. The formula is in free access, as well as software, so anybody can see what it does.