Sorry I didn't understand that bit :)
Reference tasks allow you to access the same task in multiple locations within a single tasklist.
1. Create tasks A, B, and C
2. Select task A
3. 'Edit > Copy'
4. Select task C
5. 'Edit > Paste as reference'
Now task C contains a reference to task A which allows task A to be edited from within task C.
This is useful if you have an action that affects 2 (or more) branches in your tasklist.