In Aboard a Task can have a parent and child like relationship where the child task will be blocked until the parent task is completed.
Go to Program
or Journey
Add
or Edit
a task
Check Trigger this task after another task
Select a parent task
How it looks in Timeline view:
How it looks from Tasks
:
When a child task is deleted, the relation with its parent will be severed.
When a parent task is deleted, there will be options to choose which child tasks to be deleted and/or orphaned.