Within a cryptocurrency network, only miners can confirm transactions by solving a cryptographic puzzle. They take transactions, mark them as legitimate and spread them across the network. Afterwards, every node of the network adds it to its database. Once the transaction is confirmed it becomes unforgeable and irreversible and a miner receives a reward, plus the transaction fees.
An investor can profit from the difference between two interest rates in two different economies by buying the currency with the higher interest rate and shorting the currency with the lower interest rate. Prior to the 2008 financial crisis, it was very common to short the Japanese yen (JPY) and buy British pounds (GBP) because the interest rate differential was very large. This strategy is sometimes referred to as a "carry trade."
For trading purposes, the first currency listed in the pair is always the directional currency on a forex price chart. If you pull up a chart of the EUR/USD, and the price is moving higher, it means the EUR is moving higher relative to the USD. If the price on the chart is falling, then the EUR is declining in value relative to the USD. The attached chart shows this.