Sometimes you’ll need to use the information you get with one of WPs functions. To get the author url you’d use $link = get_author_posts_url($users['ID']); https://codex.wordpress.org/Function_Reference/get_author_posts_url
As far as checks
if (get_the_author_meta('twitter')) {
?>
<p>
<a href="http://twitter.com/<?php
echo the_author_meta( 'twitter' ); ?>" target="_blank">@<?php
echo the_author_meta( 'twitter' ); ?></a>
</p>
<?php
} // end if get twitter
Also, I’m not sure, but you may need to supply the author ID in this case https://developer.wordpress.org/reference/functions/get_the_author_meta/ and https://codex.wordpress.org/Function_Reference/the_author_meta
