The Select field will add a dropdown select box of choices for the content writers to pick from.
Here's an example of how to integrate the selected text value. In this case the Select field has the API ID of category
.
php (sdk v4 or later):
<p><?= $document->data->category ?></p>
php (sdk v3 or earlier):
<p><?= $document->getText('page.category') ?></p>