How do I assign tasks to users?
You can assign tasks to any member of a shared list, including yourself. To assign a task within a shared list, open the task's detail view and select Assign to. Then, select the member of the shared list you'd like to assign the task to. In To Do on Windows, you can assign tasks while creating them.
What is the best way to assign tasks?
Assign based on preference
So it could be good to assign tasks at a meeting with the team. As you discuss priorities, deadlines, and availability, ask them which tasks they would like to work on. If someone shows interest in a specific type of work, they should (with some consideration), be allowed to take it.