Supernatural Skip

Sorry for skipping over seasons 3 and 4 but there are only like a few things that are need to know.
At the end of season 3 Dean fords and goes to Hell. Sam learns that he is immune to the " demon light" that can kill every one.
In season 4 Dean is drag out of Hell by an angel of The Lord named Castiel, but after Dean starts torturing other souls which breaks the first of 66 seals that will break Lucifer free of his cage.
Through the season the brothers are trying to stop Lilith, the first demon. From breaking seals and dealing with Sam's demon powers.
In the end of season 4, Dean is be held by Zachariah in the so called "green room" which is really a room that looks like the pope's office. Dean is told by Castiel that Lilith is the final seals, meaning they can not kill her, but Zachariah wants Lucifer to come. Elsewhere Sam is getting ready to kill Lilith not knowing that she is the final seals. Ruby, his demon girlfriend , knows this but does not tell him because she wants Lucifer to come as well. All in all Sam kills Lilith and lets Lucifer loose on Earth. While the cage is opening "God" transports Sam and Dean out of harms way.
This is where season 5 starts. This is not my favorite season but I still love it, so lets take on the Apocalypse.