The currency that you are purchasing is called quote currency. In forex trading, you sell one currency to purchase another. The exchange rate tells you how much you have to spend in quote currency to purchase base currency. A long position means that you want to buy the base currency and sell the quote currency.
In our example above, you would want to sell U. A short position means that you want to buy quote currency and sell base currency. In other words, you would sell British pounds and purchase U. The bid price is the price at which your broker is willing to buy base currency in exchange for quote currency. The bid is the best price at which you are willing to sell your quote currency on the market.