A cryptocurrency exchange is a place where you can exchange fiat currencies (like CAD, USD, EUR, etc) for cryptocurrencies (Bitcoin, Ethereum, Litecoin, etc.) and vice versa.
An exchange also provides its users with a digital wallet to carry any cryptocurrency they may purchase. The exchange is responsible for the security of any wallets provided to their users. If cryptocurrency is withdrawn off the exchange and into the user’s own personal wallet, then the security of the wallet is the responsibility of the user.