Trade is volunteering to exchange one thing for another.
Trade increases the wealth of both parties because they are both exchanging something that they have for something that they want more.
Example 1: A fruit vendor gladly exchanges a piece of fruit for your money when they have more fruit than they want and less money than they want. And you will gladly exchange your money for a piece of fruit when you would rather eat a piece of fruit than keep that money in your pocket or bank account.
Example 2: An employee voluntarily exchanges their time, attention and effort in return for a salary when they have surplus time and a lack of money. And an employer gladly employs people when they have surplus money and not enough people to run their business.
Participating in trade is the only way that billions of people can build wealth and escape poverty (and we must have free markets if everyone is going to participate in trade).