Any and all sins they have committed are up for confession, but most importantly they must confess mortal sins. Things like sexual immorality, killing, etc. There are a lot of things that fall into this area. These sins are ones that cut us off from God and His grace. We are to be forgiven these before receiving Communion/Eucharist thus we receive an outpouring of grace again. Of course we can’t remember all the little things, but they are always good to confess if we can remember them. One must examine their conscience before confessing to make a good confession. I am sure you can find a thread on mortal/venial sins to find the differences.
Well, I wouldn’t know, but if there is no confessional then I would say that the likelihood of being behind a screen would be rare. Especially since it is not the norm in the Anglican Church.
Face to face confession isn’t bad at all…it’s really liberating to be able to talk to your priest in confession, and know that he will keep it to himself forever. Keep this in mind, he has probably hear it a million times before and probably heard worse.