how did you get there / background
For me, engineering was the path that led to being a PM. I was a decent developer, but always found myself more interested in what we should be building opposed to how to build it. Background includes BS computer eng, masters in systems eng and an mba. Did software dev for years and gravitated toward roles that increasingly positioned me for PMing while getting those last two degrees.
"junior product" positions
There are junior product positions, just very few. Google/Twitter have an APM program. At FB it is the RPM program. There are many paths that lead to being a PM. Look for stepping stones and be persistent. I know PMs that were previously a software developer, product marketing manager, project manager, technical program manager, designer, etc. If you are able to take on one of those roles at a company that also has PMs, you can probably work towards a transition.
skills
In terms of skills, this thread on Quora is good, especially Ian McAllister's response: https://www.quora.com/What-distinguishes-the-Top-1-of-Produc... Keep in mind that different companies will put more or less weight on a particular competency. e.g. Google requires PMs to have a technical background will ask technical questions, facebook does not. Facebook will ask a lot of questions around data, experimentation, data-driven decision making, etc. because they are a very data driven culture.