How do you put JavaScript into an HTML document?

[FanofMedicine]

Hi! I am just beginning to learn web design on my own. So I am messing around with Notepad++ and my website is offline, but the design is cool.

I want to add on a countdown clock timer that ends on August 1st, but I was searching online and people are saying that it is a Javascript language thing.

Is there any way you can insert Javascript countdown timers into HTML documents?

Thanks!