The main types of orders in forex trading are market order, limit order and stop loss order.
A market order is an order to take a trade in a currency pair at the current market price. Unless you specify otherwise, your broker will enter your order as a market order.
The advantage of a market order is that you are almost always guaranteed your order will be filled (as long as the market is deep enough so there are buyers and sellers).
For example, let's assume you want to buy EUR/JPY which is currently trading at 135.46 (bid)/ 135.50 (ask). If you want to buy at these levels, you click on "buy" (ask) and your forex trading platform will immediately execute your market order. If the market is very volatile and prices fluctuate wildly, you will see a message pop up on your screen asking you something to the effect of "The price has changed. Would you like to buy at 135.54?" That's what's called re-quoting. There's a way to get the platform not to give you re-quotes, but to fill the order at the next best price. Ask your broker for more information.