Base and quote currency
The first currency listed in a forex pair is called the base currency, and the second currency is called the quote currency. The price of a forex pair is how much one unit of the base currency is worth in the quote currency.
So in this example, GBP is the base currency and USD is the quote currency. If GBP/USD is trading at 1.35361, then one pound is worth 1.35361 dollars.
If the pound rises against the dollar, then a single pound will be worth more dollars and the pair’s price will increase. If it drops, the pair’s price will decrease. So if you think that the base currency in a pair is likely to strengthen against the quote currency, you can buy the pair (going long). If you think it will weaken, you can sell the pair (going short).