Choose the list you want to share. On the main screen, click on your user icon in that list's box. In the sharing screen, invite your friends to share the list with you by inserting their email in the text box, pressing enter and then clicking 'Send Invitations' at the bottom of the screen. If your friends are already using Any.do, they will receive a notification that you have shared a list with them. If not, an email will be sent to their inbox.