Can someone help!

Where do you add text to customise the 404 Page

<?php get_header(); ?>

<div class="container-wrap">

<div class="container main-content">

<div class="row">

<div class="col span_12">

<div class="col span_12 section-title">

<form role="search" method="get" class="search-form" action="<?php echo home_url( '/' ); ?>">

<label>

<input type="text" class="search-field" placeholder="<?php echo __('Search...', NECTAR_THEME_NAME); ?>" value="" name="s" title="<?php echo __('Search for:', NECTAR_THEME_NAME); ?>" />

</label>

<input type="submit" class="search-submit" value="<?php echo __('Search', NECTAR_THEME_NAME); ?>" />

</form>

</div>

</div>

</div>

</div><!--/row-->

</div><!--/container-->

</div><!--/container-wrap-->

<?php get_footer(); ?>