Select the task list that you'd like to share with someone and click the "Actions for tasks" icon on the right. Select "Share/Permissions" from the dropdown menu. Decide if you want to invite people by email or share a link. To invite people via email type in a name or email address in the "Invite people" box. Then click "Viewer" and select the level of permissions you'd like to assign to the person you are sharing your task with. You can also type a message if you'd like and click "Save". The person you shared your Task with will receive an email with a link to view it. To share a link, select "Anyone with the link and invited people" from the dropdown menu and click "Copy link". You can share the link via email, text, instant message, or any other way you communicate.
Tip: you can add an expiration date or a password by clicking the gear icon in the top right corner.