What's the best resource to educate myself on what my teens are doing/watching?

I'm worried that I don't know enough about what my teens are watching on youtube, or Twitch, or listening to, etc. I also don't have much visibility in to what they're doing on the apps they have on their phones. How do others deal with this? How do other parents keep up w the slang? Generally, how do parents keep up? via /r/Parenting https://ift.tt/2IIfPqr