Add member to the task

[Dmitriy Mykalo]

How can I add a member to the task without adding him to the board?

Or how can I hide all the other tasks in a board from the member?

[Matthew N]

Hey Dmitriy

In order for a member to be assigned to a card, they need to also be a member of the board.  It's not possible to hide other cards or lists from certain users on a board. When a person is a member of the board, they will see all cards on that board.