An online provider that converts a country's currency (dollars, Euros, pounds, etc.) to cryptocurrency (Bitcoin, Ethereum, etc.). Like any money exchange, a fee is taken. Bitbuy.ca, Coinbase, Kraken, Cex.io and ShapeShift are examples.
For people using cryptocurrencies as an investment rather than to obtain merchandise, any exchange can be used. However, some exchanges offer trading transactions like the stock market such as limit orders. Other platforms allow sellers to set their own exchange rate. See cryptocurrency