This availability condition makes it easy to show modules or sections only when a user completed a course. A course certificate is a good sample, but it can also be used to close discussion forums, hide quizzes or exams when a user finished a course.
Check the global documentation about conditional availability conditions : https://docs.moodle.org/en/Conditional_activities_settings
1. Unpack the zip file into the availability/condition/ directory. A new directory will be created called coursecompleted.
2. Go to Site administration > Notifications to complete the plugin installation.