At the bottom of the editor, the plugin will add a statusbar and in it a character and word count. You can check it by typing some text.
<!DOCTYPE html>
<html>
<head>
<title>Redactor</title>
<meta charset="utf-8">
<!-- css -->
<link rel="stylesheet" href="/your-folder/redactor.css" />
</head>
<body>
<!-- element -->
<textarea id="entry">...</textarea>
<!-- js -->
<script src="/your-folder/redactor.js"></script>
<script src="/your-folder/plugins/counter/counter.js"></script>
<!-- call -->
<script>
Redactor('#entry', {
plugins: ['counter']
});
</script>
</body>
</html>