A Suppression list is a list where you should include the members of your list that you never want to be added to it again and never send them any of your future newsletters. Keep in mind that, after moving said members to this list, you won't be able to ever add them to any of your email lists in the future.
Now let's see exactly how you can add members to your Suppression List:
1. At the top of your Dashboard page, hover your mouse over the Audience tab to reveal the drop-down menu, and then click on the Email lists option.
2. Click on the name of the email list, whose member(s) you wish to add to your suppression list.
3. Once inside your email list, tap on the View all members button.
4. Click on the corresponding check-box on the left of the member's Email.
5. On the Select Action menu that appears above your member's Email, select Add to suppression list.
Alternatively, you can perform the same action by clicking on the three-dots menu on the right of your member's data.
6. If you would like to check that your member has been successfully moved to your Suppression List, tap on the Account icon on the right top corner of your account and then choose the Suppression List option on the menu appearing.
Once inside your Suppression List, you can view all the members contained in it.
Moreover, you can permanently delete the members that exist in your Suppression List.