How a Forex trade works
Every currency pair has two prices: the bid (what you can sell at) and the ask (what you can buy at). The tiny difference between them is the spread — a cost of trading.
If you believe EUR/USD will rise, you buy (go long). If you believe it will fall, you sell (go short). Your profit or loss is the difference between your entry and exit price, multiplied by your position size.
A simple example
You buy EUR/USD at 1.1000 and it rises to 1.1050. That is a 50-pip gain. On a 1-lot position, each pip is about $10 — so that is roughly $500 profit.
The reverse is also true: if it falls to 1.0950, you lose about $500. This is why risk management (Module 5) is the most important skill you will learn.