I agree with @kiwiupover and @ankurk just dive into Ember. It could be helpful to experiment with Backbone, to understand the differences but by no means a prerequisite. But these days it seems everybody is comparing Ember and Angular. By comparison Backbone is a relatively lightweight framework the source is less than 2000 lines of code. The concensus seems to be that starting with Backbone you will just end up eventually recreating many of the things that are already baked into these larger frameworks. So why not just start with the framework you want to use?
Frameworks are all about conveniences. And every one is going to tackle common problems in a specific way. It can be helpful to try and compare frameworks, but probably don’t have to think of them in terms of hierarchy. Where one is a prerequisite for another. I don’t think the frameworks are designed with that intent in mind.