Как из такой html разметки реализовать поиск на сайте?

<form method="post">
    <input type="hidden" name="do" value="search">
        <input type="hidden" name="subaction" value="search">
</form>

<form method="post">
<input type="hidden" name="do" value="search">
<input type="hidden" name="subaction" value="search">
<div id="main-search_input">
   <div class="input-group col-md-12">
      <input type="text" id="search" class="form-control input-lg" placeholder="Поиск" />
         <span class="input-group-btn">
            <button class="btn btn-info btn-lg" type="button" id="submit">
               <i class="fa fa-search"></i>
            </button>
         </span>
      </div>
</div>
</form>