Explaining code

im new in JavaScript. I really like gallery that i found on w3school site, unfortunately they didn’t explained how it works. Can somebody please explain to me how this code works?

var slideIndex = 1;

// Next/previous controls
function plusSlides(n) {
  showSlides(slideIndex += n);

// Thumbnail image controls
function currentSlide(n) {
  showSlides(slideIndex = n);

function showSlides(n) {
  var i;
  var slides = document.getElementsByClassName("mySlides");
  var dots = document.getElementsByClassName("demo");
  var captionText = document.getElementById("caption");
  if (n > slides.length) {slideIndex = 1}
  if (n < 1) {slideIndex = slides.length}
  for (i = 0; i < slides.length; i++) {
    slides[i].style.display = "none";
  for (i = 0; i < dots.length; i++) {
    dots[i].className = dots[i].className.replace(" active", "");
  slides[slideIndex-1].style.display = "block";
  dots[slideIndex-1].className += " active";
  captionText.innerHTML = dots[slideIndex-1].alt;

for more information here is link to this gallery on w3chool

why don’t you explain what you understand so it is possible to focus only on what you are missing?

Honestly the whole js is hard to understand for me.

Have you gone through the JavaScript curriculum on FCC?

Im learning js for a while yet still this code is hard to understand. I can just copy and paste that block of code but i was hoping someone can explain it to me first.