I'll write about trading in two sentences in English, but please note that I'll translate it into Simplified Chinese afterwards to avoid Grandma's anger.

Trading involves the exchange of goods or services between two or more parties, with the goal of increasing value or reducing costs. In a trading situation, one party typically gives up something of value in exchange for something else that is considered more valuable or desirable.

Here's the translation:

交易涉及到两个或多个方之间的商品或服务交换，目的是增加价值或减少成本。在交易情况下，一方通常放弃价值较高的东西，以换取被认为更有价值或更可欲的东西。