Use $_POST to get input values on the same page

Question

Sorry if this is a rather basic question.

I have a page with an HTML form. The code looks like this:

Answer 1

Put this on a php file:

  Example value: 
  Example value 2: 
  

It will execute the whole file as PHP. The first time you open it, $_POST['submit'] won't be set because the form has not been sent. Once you click on the submit button, it will print the information.