Typically, require() means that you're 'requiring' something that you want to use in your project. You'll usually set it to a variable (var) or constant (const), then use that variable or constant to call whatever it is that you're requiring. Like in Node.js, there are different modules that you set to a require(). Then I'll use the 'http' module or 'tcp'/'net' module, for example, to build a small server.

Here's an example of how to use require(), based on the link you posted:

var aframe = require('aframe');
var aframeComponent = require('aframe-event-set-component');

Hopefully this helps.....I'm sure you'll get other responses from others that probably know more than I do :)