You can try using Bootstrap or any other CSS library like Semantic UI, Materialise etc.
In Bootstrap, this can look like this:
<form class="form-inline">
  <label class="sr-only" for="inlineFormInputGroupUsername2">Username</label>
  <div class="input-group mb-2 mr-sm-2">
    <div class="input-group-prepend">
      <div class="input-group-text">
        <i class="fa fa-at"></i> <!-- Use of font awesome icon -->
      </div>
    </div>
    <input type="text" class="form-control" id="inlineFormInputGroupUsername2" placeholder="Username">
  </div>
</form>
To add icon at the end of input field:
<form class="form-inline">
  <label class="sr-only" for="inlineFormInputGroupUsername2">Username</label>
  <div class="input-group mb-2 mr-sm-2">
    <input type="text" class="form-control" id="inlineFormInputGroupUsername2" placeholder="Username">
    <div class="input-group-append">
      <div class="input-group-text">
        <i class="fa fa-at"></i>
      </div>
    </div>
  </div>
</form>
See an example at Codepen