Happy to someone new in the crypto space! I think I’ll give you a fairly short answer to help you understand the concept better.
Bitcoin is basically a digital currency. Well, it was initially released as a currency, but today it’s seen more like a tradable asset or store of value, like gold.
The story behind Bitcoin is that in 2008, a person or group of people named Satoshi Nakamoto published a document on a peer-to-peer currency system. The background for this was pf course the economic crisis in the us that affected the global economy. Through bitcoin, Nakamoto also introduced a new technology called blockchain technology. Blockchain is basically a highly secure distributed ledger system.
Although Satoshi Nakamoto created Bitcoin, the system is completely run by the people. It is decentralized.
The legality of Bitcoin would depend on where you live and what the regulatory compliance in your country is. Hope this helps.