Bitcoins can be bought on exchanges that exchange fiat money for Bitcoins. The exchanges generate a unique Bitcoin Address for the user from which Bitcoins can be withdrawn to store in cold or hot storage wallets or sent to make payment anywhere across the world. There are over 3.5K Bitcoin ATMs around the world similar to the All Teller Machiner (ATM) of banks; the number has increased every year since its invention in 2014. The ATM users must have their own Bitcoin Wallets. Bitcoin exchanges on the other hand provide an online portal, Coinbase and Bitfinex are the biggest in terms of volume. There are a plethora of other Bitcoin exchanges around the world; the limitations to trade (buy/sell) are imposed by Government regulations. Some countries like China and Russia have imposed binding restrictions on its use and trade. Whereas, US, Japan and Canada have accepted it in all forms (payment system or trading).
The exchanges provide a Bitcoin address for the user after sign up and verification. This wallet can be used to deposit, withdraw or even withhold Bitcoins. The exchanges have the rights to the private address of Bitcoin and this makes the user vulnerable to cyber attacks, though theses exchanges have evolves over time. Two-factor Authentication and email confirmation are some of the modern day programming techniques that the exchanges use to secure funds. Some of the exchanges are as old as Bitcoin. Bitfinex cold wallet has a balance of 134,474 Bitcoins as of October 2018.