Sub Tasks

Intervals does not feature traditional subtasks but milestones can be used in a very similar fashion. With milestones tasks become a child (or subtask) of its milestone and milestones do have quasi dependencies since you can group tasks together with one milestone and use the milestone to move all of the tasks that are associated with it. This video overview of milestones might be worth a look https://www.myintervals.com/video/#Milestones if you haven't experimented with milestones much.

Regarding dependencies, Intervals does not include traditional task dependencies (Finish to Start, Start to Start, Lag, Lead, etc.) like MS Project or other software based on the waterfall method. This is done primarily to accommodate a wide range of work flows and Intervals is built out of an iterative philosophy very similar to Agile development (https://en.wikipedia.org/wiki/Agile_software_development | https://en.wikipedia.org/wiki/Agile_Manifesto) where tasks take a more free style approach.