Learn to start looking up docs. This is all basic JS for interacting with the DOM (the virtual representation of the page in the browser). Here it talks about addEventListener.
This takes a selector (a variable holding a reference to something in the DOM) that was probably defined earlier to add and event listener it is listening for a mouse click and when that happens it will fire a function called showResults that was defined elsewhere. This is how you get mouse clicks to run JS.
const quizContainer = document.getElementById('quiz');
This is defining a new selector, it is looking in the DOM for an element with and id of “quiz”.
I can understand your impatience, but you also have to understand that these things take time. You might try and tackle the Random Quote Machine or something in that category.
As to the general concepts, things like this might help. That and look up keywords on youtube and follow along. If you get stuck on something, google it and if you can’t find it check the forum. Just be very specific.