Why currencies come in pairs
You cannot buy a currency without selling another, so every forex quote involves two currencies — a pair. EUR/USD means euros priced in US dollars. When you "buy" the pair, you are buying euros and selling dollars at the same time.
This two-sided nature confuses newcomers because it means every trade is simultaneously a bet for one currency and against another. There is no neutral position; you are always expressing a relative view.
Majors, minors, and exotics
The "majors" are the most heavily traded pairs, all involving the US dollar against another large economy's currency, such as EUR/USD, GBP/USD, USD/JPY, and USD/CHF. These tend to have the tightest spreads and the deepest liquidity.
"Minors", or crosses, pair two major currencies without the dollar, like EUR/GBP or EUR/JPY. "Exotics" pair a major currency with a smaller or emerging-market currency. Exotics usually have much wider spreads and can move violently, which makes them a poor place for beginners to learn.
What to trade while learning
For most beginners, sticking to one or two majors is the sensible choice. Their tighter spreads lower your trading costs, and their behaviour, while never predictable, is at least widely studied and comparatively orderly.
Exotic pairs can tempt people with big daily ranges, but wide spreads and sudden gaps make them expensive and unforgiving. Master the calmer pairs first; the exotics will still be there later if you ever genuinely need them.