Trouble figuring out slider for post containers

There is a section on the site I’m working on that loads 4 containers that are links to posts. I need to add functionality that allows you to scroll through more containers in the section by clicking right or left arrows. Below is a screenshot of what it needs to be like (It looks exactly the same now, without the arrows and sliding functionality). I tried using http://flexslider.woothemes.com/ but had trouble using it. I followed the directions, but it didn’t seem to work. If anyone could help me out or give me any advice it would be very appreciated!

What I am trying to do:

HTML:

<div class="opinion">
  <div class="wrap">
    <div class="atable">
        <div class="acell">
          <div class="contentbox">

            <ul class="slides">
              <li><a href="www.google.com" style="background-image:url('https://upload.wikimedia.org/wikipedia/commons/8/8f/Hippie-flower_-_Virginia_-_ForestWander.jpg');"><img class="slideImg" src="https://upload.wikimedia.org/wikipedia/commons/8/8f/Hippie-flower_-_Virginia_-_ForestWander.jpg" /><span>Flower</span></a></li>
              <li><a href="www.google.com" style="background-image:url('https://upload.wikimedia.org/wikipedia/commons/8/8f/Hippie-flower_-_Virginia_-_ForestWander.jpg');"><img class="slideImg" src="https://upload.wikimedia.org/wikipedia/commons/8/8f/Hippie-flower_-_Virginia_-_ForestWander.jpg" /><span>Flower</span></a></li>
              <li><a href="www.google.com" style="background-image:url('https://upload.wikimedia.org/wikipedia/commons/8/8f/Hippie-flower_-_Virginia_-_ForestWander.jpg');"><img class="slideImg" src="https://upload.wikimedia.org/wikipedia/commons/8/8f/Hippie-flower_-_Virginia_-_ForestWander.jpg" /><span>Flower</span></a></li>
              <li><a href="www.google.com" style="background-image:url('https://upload.wikimedia.org/wikipedia/commons/8/8f/Hippie-flower_-_Virginia_-_ForestWander.jpg');"><img class="slideImg" src="https://upload.wikimedia.org/wikipedia/commons/8/8f/Hippie-flower_-_Virginia_-_ForestWander.jpg" /><span>Flower</span></a></li>
              <li><a href="www.google.com" style="background-image:url('https://upload.wikimedia.org/wikipedia/commons/8/8f/Hippie-flower_-_Virginia_-_ForestWander.jpg');"><img class="slideImg" src="https://upload.wikimedia.org/wikipedia/commons/8/8f/Hippie-flower_-_Virginia_-_ForestWander.jpg" /><span>Flower</span></a></li>
            </ul>

          </div>
        </div>
      <?php endwhile; wp_reset_query(); ?>
    </div>
  </div>
</div>

CSS:

.opinion {
  background-color: #fff;
  font-size: .8em;
  padding-top: 25px;
  padding-bottom: 25px;
}

.opinion:after {
  clear: both;
  content: "";
  display: block;
}

.opinion .atable {
  display: table;
  border-collapse: separate;
  border: 0px;
  padding: 0px;
  outline: none;
  border-spacing: 1em;
  width: 100%;
  table-layout: fixed;
}

.opinion .atable .acell {
  display: table-cell;
  height: 100%;
  width: 25%;
  overflow: hidden;
  border-radius: 3px;
  -webkit-border-radius: 3px;
  -moz-border-radius: 3px;
  border: 1px solid #ccc;
  background-color: #fff;
  outline: none;
  vertical-align: top;
}

.opinion .atable .acell:hover {
  -webkit-box-shadow: 0px 5px 7px 0px rgba(50, 50, 50, 0.25);
  -moz-box-shadow: 0px 5px 7px 0px rgba(50, 50, 50, 0.25);
  box-shadow: 0px 5px 7px 0px rgba(50, 50, 50, 0.25);
}

.opinion .atable .acell:last-child {
  margin: 0px;
}

div.opinion .atable .acell .contentbox ul {
  padding: 0;
  min-width: 40px;
  widows: 100%;
  margin: 0;
}

div.opinion ul.slides li:hover:after {
  display: block;
  width: calc(100% - 20px);
  height: calc(100% - 20px);
  left: 9px;
  top: 9px;
  position: absolute;
  border: 1px solid white;
  content: ' ';
  pointer-events: none;
}
div.opinion .atable .acell .contentbox ul li a span {
    padding: 20px;
}

.opinion .atable .acell .contentbox ul.slides:hover a>span {
  position: absolute;
  bottom: 0px;
  left: 0px;
  padding: 20px;
  color: #fff;
  z-index: 10;
  display: inline-block;
}

.opinion .atable .acell .contentbox {
  position: relative;
}

.slideImg {
  display: none;
}

.opinion .atable .acell .contentbox ul {
  list-style-type: none;
}

.opinion .atable .acell .contentbox ul li a {
  color: white;
  display: block;
  height: 200px;
  max-width: 100%;
  width: 100%;
  background-size:cover;
  background-position:center;
}

.opinion .atable .acell .contentbox ul li a span {
  position: absolute;
  bottom: 0px;
  left: 0px;
  padding: 10px 10px 20px 10px;
  color: #fff;
  z-index: 10;
  display: inline-block;
  font-size: 1.3em;
  text-shadow: 1px 1px 1px #000;
  -webkit-border-top-left-radius: 4px;
  -moz-border-radius-topleft: 4px;
  border-top-left-radius: 4px;
}

.opinion .atable .acell .contentbox ul li a:after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  box-shadow: inset 0 0 0 350px blue;
  width: 100%;
  height: auto;
}