Check out example codes for "slideshow in html". It will help you in understanding the concepts better.

Code Example 1

* {box-sizing:border-box}

/* Slideshow container */
.slideshow-container {
  max-width: 1000px;
  position: 
relative;
  margin: auto;
}

/* Hide the images by default */
.mySlides {
  display: none;
}

/* Next & previous buttons */

.prev, .next {
  
cursor: pointer;
  position: absolute;
  
top: 50%;
  width: auto;
  margin-top: -22px;
  padding: 16px;
  color: 
white;
  font-weight: bold;
  font-size: 18px;
  
transition: 0.6s ease;
  border-radius: 0 3px 3px 0;
  
  user-select: none;
}

/* 
Position the "next button" to the right */
.next {
  
right: 0;
  border-radius: 3px 0 0 3px;
}

/* On hover, add 
a black background color with a little bit see-through */
.prev:hover, .next:hover {
  
background-color: rgba(0,0,0,0.8);
}

/* Caption text */
.text {
  color: #f2f2f2;
  font-size: 15px;
  padding: 
8px 12px;
  position: absolute;
  bottom: 8px;
  
width: 100%;
  text-align: center;
}

/* Number text (1/3 
etc) */
.numbertext {
  color: #f2f2f2;
  font-size: 
12px;
  padding: 8px 12px;
  position: absolute;
  
top: 0;
}

/* The dots/bullets/indicators */
.dot {
  cursor: pointer;
  
height: 15px;
  width: 15px;
  margin: 0 2px;
  
background-color: #bbb;
  border-radius: 50%;
  display: 
inline-block;
  transition: background-color 0.6s ease;
}


.active, .dot:hover {
  background-color: #717171;
}

/* 
Fading animation */
.fade {
  -webkit-animation-name: 
fade;
  -webkit-animation-duration: 1.5s;
  animation-name: 
fade;
  animation-duration: 1.5s;
}

@-webkit-keyframes 
fade {
  from {opacity: .4} 
  to {opacity: 1}
}

@keyframes 
fade {
  from {opacity: .4} 
  to {opacity: 1}
}

Code Example 2

var slideIndex = 0;
showSlides();

function showSlides() {
  var i;

    var slides = document.getElementsByClassName("mySlides");
  
for (i = 0; i < slides.length; i++) {
    
slides[i].style.display = "none"; 
  }
  slideIndex++;

    if (slideIndex > slides.length) {slideIndex 
= 1} 
  slides[slideIndex-1].style.display = "block";

  setTimeout(showSlides, 2000); // Change image every 2 
seconds
}

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