For recurring priced products (memberships) you can choose to create a free trial and/or a coupon.
If you create a free trial, it will be applied to everyone who joins your recurring product.
If you create a coupon, the coupon discount will be applied to only those who redeem the coupon.
What if I have a trial AND a coupon?
The coupon discount will be applied after the duration of the trial.
For example, if you have a 1-month free trial and a coupon for 1-month free, the student will have 2-months free (1-month free trial + 1-month free from the coupon) and will be charged full price in month 3.
Or if you have a 1-week free trial and coupon for 1-month free coupon, the student will have 5-weeks free (1-week free trial + 4-weeks free from the coupon) and then will be charged full price.