Bitcoin is using the Blockchain.
Blockchain is actually a lot of transactions (blocks) that are connected like a chain. Because the new block that a user will request have all the code of the previous blocks. So that no one can change the code (fraud) and earn illegal money.
Solidity is the name of the language that Ethereum uses.
Its not. Bitcoin Core and most other cryptocurrencies are "written" in C++. If you don't understand blockchain and cryptography itself and how this all works, please, don't try to create something based on it. I don't want to be toxic and negative, but its way harder than you might think.
