Did you grow your own sugar? Did you build your own laptop? Maybe, but odds are you didn't. You almost certainly traded money for sugar and your laptop.
We buy things because we don't have the time, resources or know-how to make them ourselves. Heck, sometimes, we're just too lazy, (thank God for Domino's Pizza). A sensible person will always buy a product if it's cheaper than making it himself.
This is why countries trade as well. A nation will buy goods from another if it is cheaper than making them at home.
I like free trade. You should, too.