How would I go about implementing a search bar with a filter, just like the one mentioned here: bootstrap amazon style search bar

All the ones I see on bootstraps page refers to drop down lists with redirects, not select lists:
This is what I have so far but it doesn't look that great and I am unsure if I am doing it correctly.
<div class="col-md-9 col-md-push-1 ">
    <h3 class="text-center">Manage Users</h3>
    <div class="container">
        <div class="row">
            <div class="col-xs-8 col-xs-offset-2">
                <div class="input-group">
                    <div class="input-group-btn search-panel">
                        <select class="btn btn-default dropdown-toggle" data-toggle="dropdown">
                            <option>All</option>
                            <option>Username</option>
                            <option>Email</option>
                            <option>Student Code</option>
                        </select>
                    </div>
                    <input type="hidden" name="search_param" value="all" id="search_param">
                    <input type="text" class="form-control" name="x" placeholder="Search term...">
                    <span class="input-group-btn">
                        <button class="btn btn-default" type="button"><span class="glyphicon glyphicon-search"></span></button>
                    </span>
                </div>
            </div>
        </div>
    </div>
</div>
