A grey notes button should automatically be added to your admin bar once the plugin has been activated. Note that the button only appears on the front end of the site and not in the admin area.
I am actually doing some updates to the plugin that I’m hoping to push live soon, if you could visit this site https://www.whatsmybrowser.org/
click on the green copy button and paste the copied URL here that will help, also what version of WordPress are you running?
Are you using any plugins that have any affect on the admin bar?
If you could list the plugins you are using I can check to see if there are any conflicts occurring.
Thanks!