I had complete ownership of a standalone scaling module I was building with engineers but plenty of guidance from my mentor and manager, both of whom had been PMs for a long time. I drew up my own blueprints/spec and occasionally hosted my own meetings.
The level of ownership really depends on your team. My team gave us full ownership where we came up with the idea for a prototype we felt was needed in our app, designed it, developed it, and kept ourselves on track. Some other teams already know what feature they want you to build but beyond that you work with your manager to set your own schedule and develop it yourself. Of course you will have a Dev mentor and PM mentor who are always there for you to ask questions to (and there will be lots of questions)!