There are several parts in the creation of a list: basic information, subscribers, welcome and unsubscribe emails.
List Name : Name of your list. This name will be displayed to the subscribers
Active : AcyMailing will never send Newsletters to a list which is not enabled. A user can't subscribe nor see a list which is not enabled.
Color : Each list has its own color so that you can easily and quickly identify it on the backend. This color is not displayed on the front-end but helps you manage your lists efficiently.
Tags : You can add tags to the lists you create, to be able to filter them afterwards on the listings where they are displayed.
On the second step you'll find a list of all the users subscribed to this list, and you will be able to add some users from there. You can also unsubscribe the users manually by clicking the icon on the right.
If you created some templates of type "welcome" or "Unsubscribe", you will see them on those two steps. You can also create one directly from here with the "Plus" button.
If you specify a welcome email, the users will receive it uppon subscribing to the list. If you manually subscribe a user to the list from the admin part of your site, the user will not receive this welcome message.
The unsubscribe email works the exact same way: when the user unsubscribes from the list, he receives this email.