Ask HN: Best places to get technical help?

Reply - If I have a problem with <technology> a good place to read/learn about it is <resource>, the best place to ask questions(forum) is <resource>.

Hopefully this makes sense.

I'm currently working on a project that has snowballed into many technologies that I have a reasonably shallow understanding of. It would be great to know where to find answers and ask questions more generally.

I don't want to limit responses to just my problems though so feel free to contribute anything you think fits this format. I'm particurality interested in finding the active communities around technologies and where they hang out.

An opinionated example from me would be: ROS (robot operating system), the construct sim, ros discourse

If anyone could inform me of some good Postgres resources that would also be awesome.