What's the difference between assigning a To-Do and attaching a To-Do?
In short: To-Do List items are assigned to Batchbook account users and attached to a record in your account. To-Dos can be attached to contacts, communications, and deals.
When you add a To-Do, you can assign it to any Batchbook account user (including yourself). If you assign that To-Do to someone else, it will appear in their To-Do List, under their To-Dos Assigned to Me display. You can still see To-Do List items you assigned to other users by selecting To-Dos I've Assigned from the pull-down menu.
Attaching a To-Do List item is just a way to connect a record with your To-Do task. For example, if you need to call Bill Withers, then you'd create a To-Do to "Call Bill" and attach it to the Bill Withers contact record in your account. That way, when the "Call Bill" To-Do appears in your To-Do List, Bill's name will, when clicked on, link to his contact detail page, where you can see his phone number and activity log.