First, click on the list you would like to share. Then, click on the button next to your initials. In the sharing screen, invite your friends to share the list by inserting their names or email address in the text box above and choosing them.
If your friends are already using Any.do, they will receive a notification in their app that you have invited them to share a list with you. If they are not already using Any.do, an email will be sent to their inbox. As soon as they accept it, you will be informed in your Notification Center.