On the team page, you will see that your school's subscription has a number of unused memberships. These are part of the package that you have purchased from Pobble. Assign these to the teachers who will be using Pobble this year.
To see this process in action, please take a look at Step 2 (38 seconds in) of the video in this article about "Transitioning to a new school year".
You will be notified if you have no memberships available. Please do get in touch with firstname.lastname@example.org if you would like to increase this amount or have any questions.