Forex Trades are for the most part Spot trades
Once the "quote" is issued by the market-maker the trader has a very limited amount of time to agree to trade. This time is usually only one or two seconds, after which the trader will not be guaranteed the same price, (exchange rate). The acceptance of the trade is done by the trader indicating either "Buy" or "Sell" and stating a quantity. Generally accepted quantities are in either hundreds or thousands or multiples of thousands.
A good, professional market-maker will guarantee the trade at the quote within several seconds. The speed of the transaction is what has made the market so busy. With an elapsed time of less than one minute per transaction, it is conceivable to make or lose a large fortune in the span of one hour or less.
Once the trade is done, you are free to ask for another quote, and to sell what you have just purchased, or to purchase "to cover" what you have just sold. There is no need to remain in the same currency pair, as the entire market is quite fluid, and you can switch any pairs to move your bank account forward on each trade.