Confused about comment "//" indicator

Link to exercise:

In step 1, the following help is given: " If you want some direction, but aren’t quite ready to check out the hint: we suggest you use the fs.readFile() method to print the contents of fileOne.txt ." The solution has the following code:

Please note the // which indicates a comment field and, I thought, was not read or executed by the computer. How is the content of fileOne printed? I had the line correct, without the “//” and it was a no-go.

The solution code did not transfer into my question:

//fs.readFile('./fileOne.txt', 'utf-8', readDataCallback);