What is JavaScript used for?

Okay, so I've been hearing about JavaScript everywhere lately, and I'm kind of confused about what it's actually used for. I mean, I know it's a programming language, but like, why is it such a big deal? I was trying to build a simple website for my friend's small business—nothing fancy, just a basic page with some info and maybe a contact form. I started with HTML and CSS, and it looked okay, but then I wanted to add a button that changes color when you hover over it, or maybe a pop-up message when someone submits the form. That's when I realized I needed something more, and everyone kept saying 'use JavaScript. ' But I have no idea where to begin. I tried watching a few YouTube tutorials, but they all jump into coding without explaining the real-world uses. Like, is it just for making websites interactive, or can it do other stuff? I've heard people talk about using it for mobile apps or even server-side things, but that sounds way over my head. Honestly, I'm a bit overwhelmed—I'm not a tech expert, just someone trying to learn this stuff in my spare time. Maybe I should have started with something simpler, but I'm determined to figure it out. Can someone break it down in simple terms? What are the main things JavaScript is used for, and maybe some examples that a beginner like me can understand? Thanks in advance for any help!