Comments are the most basic feature in programming, they are used to keep track of what something do and so explain what a piece of code do.
Writing a comment in code is the most simple stuff to do. You just write two slash // like so and the row after them will be a comment where you can write your text.

protected override void OnGameStart()
{
    // this is a comment text
}
            

If you want to do a multi-line comment you have to follow a different syntax.
The start of the comment is declared as a slash and asterisk /*, while the end of it with an asterisk and a slash */ (basically the opposite)

protected override void OnGameStart()
{
    // this is a comment text

    /*
        This is
        a multi-line
        comment
    */
}        
            

// this method gets executed right before gaining player control            
protected override void OnGameStart()
{
    // here I write what I want to do
}