Use the following working carousel slider template as a starting point (including all of the CDN files in the exact same order you see them in the template) and then start replacing parts of that template with your own content one by one.
Only do it one piece at a time and as soon as something you add breaks the whole thing, you’ll immediately know the culprit.
Here’s the working template (click the “run code snippet” button below and expand to full page):
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous"> <script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script> <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script> <div id="carouselExampleIndicators" class="carousel slide" data-ride="carousel"> <ol class="carousel-indicators"> <li data-target="#carouselExampleIndicators" data-slide-to="0" class="active"></li> <li data-target="#carouselExampleIndicators" data-slide-to="1"></li> <li data-target="#carouselExampleIndicators" data-slide-to="2"></li> </ol> <div class="carousel-inner"> <div class="carousel-item active"> <img class="d-block w-100" src="https://placeimg.com/1080/500/animals" alt="First slide"> <div class="carousel-caption d-none d-md-block"> <h5>My Caption Title (1st Image)</h5> <p>The whole caption will only show up if the screen is at least medium size.</p> </div> </div> <div class="carousel-item"> <img class="d-block w-100" src="https://placeimg.com/1080/500/arch" alt="Second slide"> </div> <div class="carousel-item"> <img class="d-block w-100" src="https://placeimg.com/1080/500/nature" alt="Third slide"> </div> </div> <a class="carousel-control-prev" href="#carouselExampleIndicators" role="button" data-slide="prev"> <span class="carousel-control-prev-icon" aria-hidden="true"></span> <span class="sr-only">Previous</span> </a> <a class="carousel-control-next" href="#carouselExampleIndicators" role="button" data-slide="next"> <span class="carousel-control-next-icon" aria-hidden="true"></span> <span class="sr-only">Next</span>