Go is a language specialized in concurrency and not parallelism.

Concurrency is the ability to handle many things at once. It is best explained with an example.

Let's consider a person running. During your morning run, let's say your shoelaces are untied. Now the person stops running, ties the shoelace and starts running again.

This is a classic example of concurrency. The person is able to run and tie shoelaces, that is, he is able to handle many things at the same time.