When I was starting out, online forums for writers were a bottomless well of information. These sites have changed over the last decade, and I am not currently active on any forums, so I suggest searching around for the site or forums that feel like the best fit for you. You can lurk and learn, or you can jump right in and start asking questions. These sites are also great places for leads when you are ready to search for an agent.
I also strongly recommend following writers, agents and editors on social media. This is the absolute best way to keep up with the tides of publishing. You’ll know which fads are hot, which ones are “so last year,” and why none of that really matters if you have a good story to tell.