Moving tasks around

Greetings everyone.

May I first congratulate the MrProject people for great work. Also for 
that patch that made subtasks not crash 0.9.1.

Then a light question: how is it possible to move tasks around in the 
Gantt chart. For instance, if project start date is changed, how could I 
  make automatic adjustments into Gantt chart (chart currently does not 
change the scheduling if project start date is changed). Also, how can I 
make an already entered task a subtask of another. I know what I need to 
do when making a /new/ subtask, but what to do with existing ones?

Thanking you,
Filip