Bitcoin is a cryptocurrency. Just like there are many different forms of currency (dollar, euro, peso, etc), there are many different flavors of cryptocurrency (Bitcoin, Etherium, Dogecoin, etc). A cryptocurrency is a digital currency that is protected by cryptography to ensure that it is secure and can not be double-spent. This is affected by the digital ledger (known as a blockchain) that keeps track of all transactions. This ledger is copied across the internet to ensure that it can not be manipulated by any single entity.
Of the many cryptocurrencies, Bitcoin is the most popular. Bitcoin was created in 2009 by a person or group named Satoshi Nakamoto. No one knows who Satoshi Nakamoto is/was, but they were the first proponents/creators of the blockchain and software that invented Bitcoin. Since then, numerous other cryptocurrencies have been created. Most of them have been created to improve upon Bitcoin. For example, Ripple has a faster transaction speed. Others have been created as a joke (Dogecoin is a high profile example of this).
The Internal Revenue Service considers cryptocurrencies to be an asset similar to gold or silver and taxes it accordingly. If you make a transaction in cryptocurrency, you are required to determine your basis in the cryptocurrency and report your gain/loss like you would the sale of any other asset. In creating a digital currency, the ultimate goal is to make it easy to use. The added real world complexities of cryptocurrency transactions are hindering it’s ability to become more mainstream.
Is a Bitcoin worth anything? Yes. It is worth what someone else is willing to pay you for it. That is the same for all currencies. Government issued currencies used to be backed by the ability to convert that currency to gold. That is no longer the case. The true value of any currency is determined by your ability to use it to obtain something else of value.
But should I invest in Bitcoin? Bitcoin is a highly speculative investment. The valuation is changing by large percentages each day. There is nothing wrong with dabbling in cryptocurrency, but until they become more mature, cryptocurrencies are closer to gambling than investing.