MemberPress is a WordPress plugin that allows you to create a members-only area of your website by gating content; it also handles the checkout process and lets you sell digital downloads.
Membership has a courses plugin that:
MemberPress Courses
Full-featured WordPress LMS.
Quick and easy activation.
Profit-driven design, optimized for student success.
Quizzes and student progress tracking.
Resettable, expireable, and shareable certificates of completion.
No complex coding.
No fiddling with pages, sub-pages, and custom post types.