Overall mental model for using Intervals as a project management software

I'm trying to quickly assess Intervals and just want to ask a question or two to see if I understand it properly. I'm coming from a mental model of project management software and running client programs of 12 to 16 weeks with phases and different kinds of work with assigned resources.

With only about an hour of assessment, Intervals seems to be a well designed interface to a relational database. For example, I would expect to set up a project with phases & tasks and assign resources to them. But what I am experiencing is one form to fill out a project form. Then another place to create tasks. In tasks I can assign them to a project. Then I might go over to milestones to which I can add some tasks that I created elsewhere. Then I can go over to Projects to drill down to see all the stuff that has been associated to it.

Is this "kind of" how Intervals works?

Is there an overall mental model that is useful to have as I try to undertstand how my organization could use this? (35 person consulting firm integrating research, business strategy & design in our client programs)

One final question, do we have to have extremely well defined tasks for Intervals to work for us or can it work at one level up of detail?

Thanks!

Chris