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