There are two options for you to share a board with: Project Members and External Team.
Learn how to create a board.
Share board with project members
The newly created board will be visible to all of the project members (excluding the external team). There’s no way to customize to selected project members.
Share board with external team
All of the members in the external team can view the tasks within in this board. If you add a task in this board, it is automatically assigned to the external team.