Bitcoin is not a cryptocurrency, it's an immutable evidence system. As a set of digital signatures on a public ledger, it's private, but not anonymous. By Bitcoin, we mean Bitcoin SV, which is the only chain running the original protocol.
One way to buy cryptocurrencies is from an exchange. You can also buy cryptocurrencies from special ATMs.
An offline mobile phone is one of the best ways to store your digital assets. Hardware wallets such as the Ledger Nano or the Trezor are also highly recommended.