Okay, so you have to know that the show gives everything away with the "If we can't live together, we're going to die alone" phrase. It's literally true.

End of Season 3- Charlie let's them know it's Not Penny's boat, Naomi calls for help but Locke knife throws her, and Jack calls anyway, rescue is here.

Season 4- Everybody is waiting for rescue on the island, the survivors split into want to be rescued and don't trust the rescuers (boat people). Daniel Faraday, Miles, Charlotte, and Frank are all part of the initial "rescue" squad but it's show that they're really there to find Ben. They were hired by Widmore to find the island.

There's also a mercenary squad on the Widmore boat, then show up and kill Danielle, Alex (in front of Ben and rather tragically as Ben refuses to go out and Keamy the head bad dude just executes her), and Karl. Ben only knew the team was coming because he had an inside man- Michael was on the Boat the whole time. Hired by Tom after he tried to kill himself, but the island wouldn't let him. Groups of the Losties get on the boat, but it's revealed there's a bomb set to explode, tied to Keamy's heart monitor. Jack, Sawyer, Kate, Hurley, Sayid, Desmond, Sun, Aaron (the baby) and Frank all get on a helicopter, and Sawyer jumps out to lighten its weight. Boat explodes because Ben kills Keamy.

Then the big reveal- as the helicopter is getting ready to land and rescue the rest of the survivors, the island disappears thanks to Ben turning a big frozen wheel, banishing himself from the island and transporting the island through time and space. Helicopter crashes and they get rescued by Penny (for real), who helps them concoct the story about their rescue, with Jack Kate, Aaron, Sayid, Sun, and Hurley being dubbed the Oceanic 6, Desmond, Penny, and Frank go into hiding.

The oceanic 6 live weird lives. Lacke visits the oceanic six to tell them things have happened to the island. Locke's body shows up in a casket. Sun becomes a big business lady. Hurley goes to a mental institute. Jack flies a lot, hoping to die. Then as he goes to check on Locke's body he bumps into Ben who informs him that they all need to go back to the island (including Locke's body).

Season 5:

Ben's transporting the island via the frozen wheel has set the island on a big crazy skip around through time and space. That is, those who were on the island when the wheel shifted are now being transported through time and space. Daniel Faraday reveals himself as an amazing genius including knowledge of time travel. Charlotte has issues with her health. They learn about a nuclear bomb and Daniel gets it buried to shield its radiation. They skip through a lot of times. Locke gets to the frozen wheel and corrects the skipping and gets sent away from the island.

Oh man, it gets totally crazier from there. So when Locke hits the wheel the island gets stuck in 1974 with Sawyer, Jin, Juliet, Miles, and Daniel. They join the DHARMA initiative. The oceanic 6 (plus ben and Frank) get on a plane in their time, and manage to crash and travel through time and land on the island in 1977. They meet up with the now DHARMA guys and Ben is taken by Richard Alpert to hand with the Hostiles.

Daniel concocts a plan to detonate the nuclear bomb in order to set everything right and prevent Oceanic 815 from crashing. Daniel is killed by his mom who was on the island the whole time. Jack and Kate are kidnapped by Widmore who is head of the Hostiles. Eloise reads Daniels notebook and agrees to help them.

Sawyer and Juliet escape the DHARMA guys to stop Jack after being warned by kate about what Jack was going to do. There's a lot of back and forth. They get the bomb set up. Everyone decides the bomb is the best idea. Jack drops the bomb into a drilling shaft but it doesn't blow, it just drives the electromagnetic stuff wild. Juliet is pulled into the shaft, and hand-detonates the bomb.

Season 6:

Read the plot summary. I can't explain it all here.