The information given above is due for an update, having that said and before saying anything else, I'll say this: I am an addict (to charmed that is....), a charmed-aholic if you please, so I'm bias about charmed related things.
I will now explain what had happened since the 3rd season had ended (plot-wise not crew....), I'm not going to say anything about earlier stuff because nothing really happened before that, meaning, almost every 1st to 3rd season episode can act as a pilot... anyway here we go.
The 4th season started with Prue's funeral, at the funeral Paige found her new step-sisters, Piper, who can blow up things, and Phoebe, foresight, she then joins them to remake the power of three, they got together to kill Shax, the source's personal hit-demon (who killed Prue BTW), they then spend the next year teaching Paige the craft (making potions and the general way of life of the witches), at some point she moves in with them.
Around the end of the 4th season they finally kill the source (at some point the source was Cole so they killed him....), and as a prize they were allowed to change their destiny and give up magic, they passed the offer, Piper is pregnant with Wyatt.
On the 5th season they met a lot of magical like creatures (not only demons... dwarves, leprechauns and the likes), Cole comes back from hell to pursue Phoebe, The sisters kills him about six month later, during the 5th season they made a lot of jokes (which doesn't sit right with it being a serious TV show), on the last episode (a double episode), they fought The Titans, killed them (with the aid of a new character {from the future}, Chris, who is also Piper's (future) second born), Leo becomes an elder, Chris does something to Leo as he orbs away (to orb - Magical power, kind of like to teleporting only with special effects that leaves a trail of light orbs behind), exactly what did Chris do stays unknown until the 6th season.
On the 6th season's opener Phoebe gets a new power, empathy, and the sisters rescue Leo from Valhalla, Leo spends half the season trying to figure out what happened to him, Piper is pregnant with Chris, all of the cast spends the rest of the time trying to find out who is going to turn Wyatt evil, on the season final, the girls find out that, one of the elders wants to kill Wyatt and accidentally turn him evil, Leo kills him, Piper gives birth to baby Chris, future Chris dies by the evil elder.
the 7th season didn't really had a good plot (which is why I said, and keep saying, that they should have pulled out the life support right then), anyway some sort of beings named Avatars urged Leo to join them, an FBI agent who knew they were evil ,(they were going to bring utopia, at the price of killing 80% of the earth population), had the only potion that can kill those things (they were uber powerful), the girls stopped the Avatars, and went on with their life now having to face an enemy named zanku who is a really powerful and smart of a demon, in the end he gets to the house and steals the girl's "book of shadows", I know the 7th season final episode wasn't aired on some places just yet, so I won't say what happened in the very end.
against my wishes (not that I have a say in this...) the show is going to have an 8th season soon, and is currently selling DVD's of each season (right now only 1st & 2nd season's but more will come soon), needless to say I will watch the 8th season and will buy the DVDs and there is nothing no one can do about it (I'm serious, stop laughing it's not funny).