Connect the JavaScript file - you will see an alert
Add a button - Make the alert only show up when you press the button
Extension
Add a text input
The button alerts you with the text you wrote
Get rid of the alert - the button updates the heading of this page
You learned all this last year. You just need to remember how!
You can Google it, ask a friend, copy from last year's work, whatever works for you.
By the end of the spell you should have some JavaScript going.