Example of JavaScript uses in websites?

Been doing plenty of research & yet still misty about the actual use of JavaScript. I know JavaScript is a client side scripting language used to validate HTML forms but is there other uses?

Like any examples of websites that uses JavaScript?

Im planning to learn JavaScript, now have mastered HTML with CSS so wanting to apply JavaScript to it. Any guides to where to start?

Some websites I know use JavaScript in Animation. But to name a few website which uses JavaScript, there is the OmniTech and WeBleedDesign.