how do you use the dependent task features

how do you use the dependent task features

I'm presuming that this is a feature for all piad subscription...but I could not figure how to create child tasks. But appart from seeing this in the right column and seeing the dependency tab in the miles and tasks view, I cannot see how I can create such things. This would add an added dimension to this software. If only I could figure out how to do it.
Darron Thevarajah