The concept is simple. Say, you have $10 worth of BTC and you want to trade it against ETH. Simply head over to the Spot market and study the price chart. If the price looks like it is particularly low and likely to go up, it may be a good time to spend a portion of your BTC to buy ETH. You place a ‘limit order’, setting the price you want to buy at, and once your order is filled and you’re in the market, you can set a limit order to make sure you sell once you’ve hit your target.
Sometimes, things may not go as expected. The price could go down instead of up, but don’t panic! Of course, you can sell if the price seems to be plummeting, but if you study the price chart well, you will notice that prices always go up and down - the market may recover over the course of several hours, days, or even weeks.