Free Trade is Freedom
Free trade does not need any more justification than freedom itself. The freedom to enter into peaceful, mutually beneficial transactions without official permission or penalty is so self-evidently a part of freedom in general that it is almost incomprehensible that anyone who purports to favor freedom over tyranny would ever argue for so-called protectionism.
You don’t need to understand the theory of comparative advantage, though it would be good for your understanding if you did. You need only favor freedom rather than state control of economic life.