Bitcoin is designed to enable peer-to-peer value exchange just like cash, but in the digital realm. This means you can trade bitcoin for anything you want, and you can do so without using intermediaries like banks or payment apps. For example, if someone paints your house, you could potentially negotiate to send them an agreed amount of bitcoin as payment. This would be effectively no different than handing over cash in exchange for the house-painting service.
Conversely, if you're looking to buy bitcoin, you could offer the seller an agreed amount of cash (or any other good or service) in exchange for the agreed amount of bitcoin.
Of course, since most people don't use bitcoin as a medium of exchange in their daily lives (at least not yet!), it's generally harder to find peer-to-peer sellers/buyers than it is to, for example, trade in local currency. This brings us to the concept of 'liquidity.'
Liquidity refers to the ease with which you can trade in and out of an asset - and it depends largely on the number of buyers and sellers (market participants) there are for an asset. Cash is typically considered the most liquid asset, as it's almost universally accepted. In other words, it's easy to exchange cash for practically anything you want. A car, by contrast, is generally a less liquid asset than cash, since it requires some effort to find a buyer. A high-end collector's car, meanwhile, would be an even less liquid asset, since the pool of potential buyers is smaller.
Bitcoin is the most liquid of all cryptocurrencies as it combines the highest number of market participants with the greatest volume of exchange. The daily exchange of bitcoin is measured in the tens of billions of dollars! Still, compared to cash, it's not liquid, particularly when it comes to using it to buy something in the real world. For this reason, there's a need for bitcoin exchanges.
A Bitcoin exchange is any service that matches buyers of bitcoin with sellers. Exchanges are what make bitcoin a liquid asset for traders at large scale.
When most people speak of Bitcoin exchanges, they're referring to centralized 'custodial' platforms like Coinbase, Kraken, and Binance. These platforms facilitate the trade of bitcoin and many other cryptocurrencies. Similar to platforms for trading stocks like Robinhood and Charles Schwab, cryptocurrency exchanges match buyers and sellers.
Critically, by definition, a centralized cryptocurrency exchange takes custody of your bitcoin. This has a number of implications relating to security, but also relating to the freedom you have to use your bitcoin as you wish.
Read more: Custodial versus non-custodial Bitcoin wallets.
From a user's perspective, the typical flow is as follows:
Make a trade by setting a 'buy order.'
Buy and sell orders are aggregated into an 'order book' which is maintained by the exchange for the purpose of efficiently and automatically matching buyers and sellers. Most exchanges allow you to set both 'market buy' orders and 'limit buy' orders. When you create a market buy order, you only need to indicate how much bitcoin you'd like to buy (you don't set the price). The exchange will automatically match you with the seller(s) currently offering the lowest price, and execute your trade. Market orders are, by and large, instantly completed, meaning the moment you submit the order, you'll receive your bitcoin in your exchange wallet/account. When you create a limit buy order, you're indicating how much bitcoin you'd like to buy and the price you're willing to pay for it. If and when there are sellers willing to accept the price you've set (your 'limit'), your order will complete, meaning your bitcoin will show up in your exchange wallet and your money (or other cryptocurrency) will disappear.
Cryptocurrency exchanges that allow you to transfer local currency to and from them are known as 'banked exchanges.' Some exchanges allow you to transfer local currency to start buying (typically in the form of credit card or payment app like PayPal), but don't allow you to withdraw local currency back to your credit card or payment app. These are known as 'partially banked' exchanges. A fully-banked exchange will allow to you fund your account via bank transfer and send local currency back to your bank account.
Generally speaking, the more users an exchange has, the greater 'market depth' it is able to provide. Market depth refers to the size of the exchange's order books. People who place buy and sell orders on exchanges are known as market makers. The more orders there are on the book, the easier it is for people to buy and sell large amounts of bitcoin at closer to the global market rate. In markets, takers are those who reduce liquidity by taking orders that are already on the books. When you place a market order, you're a taker. You can also be a taker when you place a limit order if you're order happens to match with another person's order that's already on the books.
In a word: fees. These may include some or all of the following:
Most exchanges charge a fee to withdraw bitcoin, other cryptocurrencies, and local currencies. In most cases, the fee is on a per withdrawal basis (not a percentage of the withdrawal amount). The withdrawal fees charged by exchanges tend to change frequently, often without notice.
These are typically calculated as a percentage of the trade value and often depend on whether you're the maker or the taker (see above). In most cases, makers pay lower fees than takers. The rationale for the discrepancy is that makers provide liquidity (and should, therefore, receive a discount), while takers remove liquidity (and should, therefore, be charged extra).
Some exchanges offer margin trading. This is where you borrow to increase your position, creating what's known as leverage. Exchanges that offer margin trading typically charge additional fees based on the amount borrowed and an interest rate determined by the total supply of funds available to all traders. You'll also likely be charged an additional fee if your position is liquidated.
For a centralized Bitcoin exchange, taking custody of customers' bitcoin and other cryptocurrencies has legal implications. Specifically, such exchanges are subject to the money transmitter laws in the jurisdiction in which they are legally registered.
For this reason, most centralized cryptocurrency exchanges require you to complete a registration process in which you must verify your identity before you can use the platform. Regulators impose this requirement on exchanges ostensibly to prevent money laundering, terror financing, and tax evasion. Regulators also typically require exchanges to report customer information (including trading history) upon request.
In many cases, you'll be allowed to begin using the exchange by verifying your email only. It's important to note that this 'lite verification' typically comes with considerable restrictions including limited purchase amounts, limited withdrawals, and in some cases, no withdrawals at all. Before you fund a cryptocurrency exchange with bitcoin or any other cryptocurrency, be sure to check that you'll be allowed to withdraw.
The next level of verification typically entails uploading nationally-issued identification like a passport or driver's license. In some cases you'll be asked to upload a photo of yourself holding your ID next to a piece of paper on which you've written, for example, the current date and a specific message as requested by the exchange.
Note that many exchanges exclude certain nationalities from using the exchange altogether.
A number of match-making platforms have arisen to (1) help buyers and sellers of bitcoin find each other, and (2) facilitate trades (typically with the use of escrow) without actually taking custody of the traders' bitcoin. These are known as peer-to-peer Bitcoin exchange platforms.
Peer-to-peer Bitcoin exchange platforms can be an effective way to buy and sell bitcoin, but since you must individually negotiate trades, they carry a certain level of inconvenience. For buyers, it can be difficult to quickly obtain the exact the amount of bitcoin they'd like to purchase, and to get it at competitive market rates. Sellers, meanwhile, may face legal implications depending on their jurisdiction and the volume of bitcoin involved. These factors combine to make most peer-to-peer Bitcoin exchange platforms considerably less liquid than most centralized (custodial) cryptocurrency exchanges.