The simple membership plugin will have a logout link inside the standard login widget. So when members are logged into the site, they will see the logout link inside the standard login widget (see the following image).
Manually Creating Logout Links
If you need to manually create logout links (example: to put it in the navigation menu) then you can do that using the following link:
https://www.your-domain.com/?swpm-logout=true
Replace “your-domain.com” with your actual domain name.
You can create logout links and put it anywhere on your site.