what does the ending ~는데 mean? what does the ending ~는데 mean? I hear it all the time from my students and was told it was used to indicate something as being background information. Still pretty ambiguous to me though. Please give examples that would illustrate it's many possible uses. thankyou :)

what does 이잖아 mean?

what exactly does 괜찮아요 mean and how does it differ from 알아서? I believe that 괜찮아요 is closer in meaning to the English "are you ok?" or "I'm feeling fine" whereas 알아서 is more like "do you understand?" or "yeah, no problem". Am I right? please use cultural reference points because I am living in Korea now and so that would be helpful.