The Subscription node is used to automatically add or remove contacts to or from an address book or books, or to add them to another program, based upon a program action being performed or reached.
In the case of adding to an address book, this is useful if you want to do something like automatically subscribe contacts to your regular newsletter series address book once they've reached the end of a welcome series.
In the case of removing from an address book, this is useful if you want to automatically unsubscribe contacts from your regular newsletter series address book as they approach a renewal period, in order to send them targeted renewal-focused emails instead.
In the case of adding a contact to another program, you could use it in a welcome program when you want contacts nearing the end of it to then get added into to your lead nurturing program.
Using and configuring the 'Subscription' node
To configure the subscription node, drag in the node from the side panel and drop it onto the canvas after the required action, ensuring it's attached, and then click on the node. A configuration panel will slide in from the right side of the screen.
From here, select whether you want to add contacts to selected address books, remove them from selected address books, or add them to selected programs, and then click Select address book/Select program.
The panel changes to allow you to select the address book/s or program/s of your choice (you can search for address books or programs by name at the top of the panel). You can select a single address book or program, or you can hold Ctrl to select multiple address books or programs if you wish.
After selecting an address book or program, you are taken back to the previous subscription configuration screen, where your selected address book/s or program/s are listed.
From here you can delete your selection by clicking on the red cross next to it. You can click on Select another address book/Select another program to make another selection.
Once happy with your selection, click Apply. Your node will be set and, when activated, your program will automatically add or remove contacts from your selected address book/s or add them to your selected program/s when they arrive at that point in the program.