We are using a free LMS plugin for our theme. This plugin available to WordPress.org. Link bellow –
It’s very powerful tool for creating LMS site, it’s offer you create courses, lessons, quiz etc. You can sell your courses online, students can buy courses and learn the lessons.
It has plugin support PayPal to take payment for the course, you can use others payment method using addons for this plugin.
Check out the addons available for this plugin – https://thimpress.com/wordpress/learnpress/
You can follow this plugin documentation to know how to create a new course, lesson, quiz etc.