The trading pair is simply the asset you buy against another asset, such as BTC/USDT. Choosing the right pair is very important, as some pairs provide higher liquidity or lower fees. Sometimes, it's better to trade via cross pairs instead of always going back to USDT. For example, if you have ETH and want SOL, don't sell ETH for USDT and then buy SOL; instead, check if there is an ETH/SOL pair to reduce costs. Understand your pair, and your profit will grow.