It's best to describe "man" with examples. Notice the capitlised words would translate to "man" in German.
In English, ONE would say that direct translation is not always good.
In Summer, YOU can visit the beach.
THEY say that German is a difficult language to learn.
It's used to talk generally about any random person. That's what I understand from it anyway.
It can mean they but not in the same way as "sie". The word "man" is hard to translate. Sometimes "one" works better, other times "they" does. For example, "man schläft früh hier" is translated as " they sleep early here" but it means "one sleeps early here". In German there's no difference.