Once you have installed Course Seats for LearnDash go and either edit or create the course you want to restrict under your wp-admin > LearnDash LMS > Courses.
On the individual course page click Settings. Which should show you a page like this:
Scroll down and you’ll see the course seats option like this:
Enter in the maximum number of course seats available and save.
Then when you go to the individual course page you will see the number of remaining course seats like so:
You can change the styling of the course seats box by using CSS. If you need any help with that feel free to contact our support team.