On an exchange.
ie: Coinbase. Opening an account with Coinbase is similar to opening an brokerage account. They require personal information and go through vigorous approvals like any investment brokerage or bank would do.
Face to Face buying; for people that don’t want to share their personal information, there are services to buy Bitcoins & other cryptos in person. These services connect people who will meet in person and buy Bitcoins in USD (or other Fiat currency). Example of this service is LocalBitcoins.
