index.html

<!-- import jQuery using the google CDN -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>

<script>
  $("button#fadeIn").on("click", function () {
    $(".fadedText").fadeIn();
  })
  
  $("button#fadeOut").on("click", function () {
    $(".fadedText").fadeOut();
  })
</script>

<button id="fadeIn">Fade text in</button>  
<button id="fadeOut">Fade text out</button>

<p class="fadedText">Some nice text to fade in and out</p>