You can create tasks dependencies by choosing the task to be performed first (previous task) on the dependency panel.
- Open the task dependency panel: Related tasks

- Search by name or by #numberID (by the number ID, don't forget the #)

How to be sure the task I want to link as the predecessor is the right one ?
An icon for each task of the list allows you to open it in a new browser window
On the Related tasks panel, you will be able to :
- see the status of each tasks (green/close; orange/wip; blue/new)
- open the task on a new window browser
- delete the previous task

On the Historical activity, you will be able to find when a Previous task has been added.
Notes:
- only one previous task can be added, but several tasks can follow the current one.
- you can create a relation between 2 tasks only if the 2 tasks are in the same To-Do project.
- if the current task is CLOSED only a CLOSED task can be linked as previous task.