If you want to giveaway one of your courses for free within a membership website then you can do that within Member App.
First navigate to the membership you've created within your Memberships Dashboard.
Select the membership that has the course inside that you would like to edit.
Now navigate to the 'Checkout' step.
Make sure Payment tab is selected.
Select 'One time' in in pricing options and set the price to $0 to make your course free.
Click 'Save' to store your changes.
Now your students can register to your course for free.