Why would protectionism cost jobs

Name and define three policy tools for enacting protectionism.

Economists sometimes say that protectionism is the second-best choice for dealing with any particular problem. What they mean is that there is often a policy choice that is more direct or effective for dealing with the problem—a choice that would still allow the benefits of trade to occur. Explain why protectionism is a second-best choice for helping workers as a group helping industries stay strong protecting the environment advancing national defense

Who does protectionism protect? From what does it protect them?