You can find this in help. This is clear and it is only that:
The To-do table contains all the to-dos that have been assigned to salespeople and teams. A to-do can be organizing meetings, making phone calls, and so on. You can assign as many to-dos to a salesperson or team as you want.
When you create a new to-do, you must:
-assign it to a salesperson or team.
-specify a contact and/or a campaign that the to-do involves.
You can also specify the type of to-do, the priority it has, and the date on which it should be completed.
When a to-do has been assigned to a team, it can be delegated to a salesperson within this Team. To-dos can be linked to opportunities, campaigns and can involve a segment.