Beginner -> How to include stylesheet for plugin, need help…

Heya, so I’m writing my first official WordPress plugin and I’m trying to apply styles to a div that appears when the user executes the function I wrote in their index.php file. But after following WordPress instructions it’s not applying the styles, can someone tell me what I’m doing wrong? Thanks!

function add_my_stylesheet() {
	$myStyleUrl = WP_PLUGIN_URL . '/example/style.css';
	$myStyleFile = WP_PLUGIN_DIR . '/example/style.css';

	if ( file_exists($myStyleFile) ) {
		wp_register_style('myStyleSheets', $myStyleUrl);
		wp_enqueue_style( 'myStyleSheets');
	}
}

function make_slideshow_div() {
	echo "
	<span class='slideshow-div'>Example</span>
	";
}