Course tickets allow you to sell tickets covering all dates and times in an entry. If you accept attendances mid-course then you may want to use this feature to automatically reduce the course ticket price as each date passes on the entry.
Firstly head over to your selected entry via Edit Entry then Tickets & Costs.
Then select the checkbox titled Course ticket. Make sure you've saved your entry with at least two dates before creating the course ticket.
After selecting this, you'll see a setting titled Discount past dates as shown below.
This is the value you want your course ticket to decrease for each date that passes on your course.
In this example above the course ticket is £100, and there are 10 dates for the course, so I've decided to discount by £10 for each date that passes. For example on the 5th date of the course, the ticket would cost £50 to join the remaining course (5 x £10 discounted from £100).