WordPress includes an "Admin Bar" that shows when users are logged into your site. The links in the admin bar generally provide a way for users to view their profile and do other things - but doesn't provide a good user experience as it is usually difficult to get back to the main members area.
The Admin Bar can cause some confusion for your members, and may cause some support emails to come through to you.
The best way to deal with this is to hide the admin bar. There are several plugins available in the WordPress.org plugin repository, however many of them haven't been updated or have extra bloated code or do extra things that are not needed.
We have made a simple plugin that handles this. Just download the plugin zip file and upload it to your site just like you would any other WordPress Plugin.
Once the plugin is activated, it will automatically hide the admin bar and no other action is needed. The latest version will hide the admin bar for everyone other than an Administrator.
As an alternate, you can also use this plugin which is similar.
Global Hide Toolbar - 1.6.1 (search in WP Plugins)