How can you make button do something like start playing a song or input a letter in html

Answer 1

Depending on what the "something" is, you use JavaScript to "watch" the button and when it is pressed it calls a function.
These codes might help you:

https://code.sololearn.com/WP69s5e6ksLK/?ref=app
https://code.sololearn.com/WMBJomQCTCmq/?ref=app
https://code.sololearn.com/WJ68bpHpefc5/?ref=app
https://code.sololearn.com/W2dsB3BO843Y/?ref=app
https://code.sololearn.com/WpT6B6zQa2Q5/?ref=app

Answer 2

You need to assign its onclick attribute to a JavaScript function.

Answer 3

Which "something" is it supposed to do? You could attach a function to it using Javascript or animate it with CSS.