You can buy and sell Bitcoin on cryptocurrency exchanges.
These exchanges exist online, where you can open an account, deposit money from your bank account, and then start trading by buying Bitcoin.
When you want to sell your Bitcoin, you will have the option of withdrawing it back into your bank account or converting it into another cryptocurrency.
This is a really great way for people who are not familiar with using cryptocurrencies to get started because they do not have to purchase any themselves.
All they need to do is sign up for a free account at Coinbase, which acts as an exchange or any other exchange.