1.Click on direct message.
2.Tipying user EDO
on the user search box, select and add.
3. Add @user_name
to select a user.
4. Add #board_name
to select a board project.
5. Add the task description
after the markup project.
Look at the mkarkUp table commands to add other details. Link
E.G.: % work progress or Estimate time arrival (ETA).