Forex trading is buying or selling a currency against another currency. Eg Selling USD to buy EUR or vice versa. One currency is traded for another currency at the exchange rate prevailing at that instant. People trade in currency to meet their requirements in each of these currencies.Eg. An importer in Japan, will have JPY with him, but would require to pay his consignment in USD. He approaches a bank and buys USD by paying his JPY. There are several players in Forex (FX) market, the major being banks. Banks trade in these currencies to meet their fund requirements and also to speculate in the market.Currently, 1 EUR can be bought by paying 1.1685 USD and this keeps fluctuating every instant. If a speculator buys 1 million EUR @ 1.1685 and later sells the same 1 million EUR @ 1.1686, he will make a profit of USD 100. Trading in FX happens in millions and is a very liquid market.In Crypto trading, an investor/speculator can buy any of the hundred cryptocurrencies by paying a fiat currency (Eg USD or EUR or GBP, etc). A cryptocurrency can be bought with another cryptocurrency also. Eg Buying Bitcoin by selling Ethereum.Both markets are related in a very minimal way. In FX, most of the trading happens in Fiat currency and is mostly backed by a central bank, whereas in crypto trading, it is decentralized. Volatility is much lesser in FX than in cryptocurrency. To purchase the initial cryptocurrency, the buyer has to usually pay via a Fiat currency.