A click is a sound like a sharp tap. Your dog might start barking excitedly every evening when he hears the click of your key turning in the lock. And you might click your computer mouse when you are excited about getting to another page on the web.
Click is also a verb, meaning to make the sound of a click: "Don't click your tongue at me — I can have ice cream for dinner if I want to!" You can use the word in a figurative way as well, to mean "fall suddenly into place," as when a confusing math problem finally clicks for you. Increasingly, to click is to tap on a computer icon with a mouse: "Click through to my new website!"