While summarizing the entire series to date briefly is probably impossible, I am going to try to summarize the core of what is going on in the books, for the benefit of the guy who asked for a summary, because I am insane.
Time is a wheel which rotates through the same seven ages over and over. Each time, it changes a little, and so while the same conflicts play out in each age, they play out in different ways. The world was created by the Creator, and serves as a prison for the Dark One, his ancient enemy (though the Dark One is not 'inside' the world, but it is his prison. Think of it as if the world was a balloon. The Dark One is inside the balloon, the Creator is outside the balloon, and all of the world is the actual physical 'skin' of the balloon). The Dark One wants to break the world in order to get out. The inhabitants of the world, in general, don't want this to happen for obvious reasons. As the Wheel of Time turns, it spins out Age after Age of conflicts. It seems that each age ends with an effort by the Dark One to break the world and escape his prison.
The Wheel of Time series is set in the 'Third Age' (an ultimately arbitrary distinction, given the same seven ages rotate by endlessly, but that's another argument...), but the shadow of the Second Age hangs over it. The Second Age was once a Utopia, a world of vast magical power, led by those able to tap into the Source, the font of magical power which also drives the turning of the Wheel of Time. Men and Women tap the two sides of the Source differently, but both sexes were known as Aes Sedai if they could channel, the 'Servants of All'. In this age, the Dark One was sealed away so flawlessly that its inhabitants had forgotten he even existed. Until, searching for a form of power which both men and women could use in the same ways (for the Source, the One Power, is used differently by men and women, who have different aptitudes with it), they bored a hole in the world, a hole which became a way in which the Dark One could touch the world.
As the Dark One's influence washed across the world, over the course of a century, Utopia unravelled as the darker sides of folk exerted themselves and an active conspiracy, the Friends of the Dark, worked to destroy it. The Second Age ended in blood and balefire, as the Friends of the Dark unleashed total war on a world which had forgotten what war was. The Aes Sedai were torn by internal arguments and by the defection of important leaders to the Dark. They were losing the war. So, the Dragon, Lews Therin Telamon, leader of the male Aes Sedai, decided on a desperate assault with his Hundred Companions (all male), to try to seal the hole which was letting the Dark One touch the world. The female Aes Sedai refused to go along, for their leader, Latra Posae, believed it was too risky and suicidal.
She was both right and wrong. The attack came just as thirteen of the major leaders of the Friends of the Dark were having a conference with the Dark One at the Bore. They were defeated, and sealed into the Bore when the Dragon and his companions closed it off. However, the Dark One had the last laugh, for as he went down in defeat, he laid a taint on the male side of the Source. Every male channeler on the planet gradually went mad and rampaged.
The result was the Breaking of the World. Entire nations were laid waste by rampaging male channelers before they died. Civilization collapsed, continents moved, mountains rose and fell, and the Second Age passed through the valley of death into the Third Age.
The books begin 3000 years after the end of the Second Age (more or less). Male channelers are now hunted down and 'gentled' (also called 'stilling', this removes their ability to channel. It can be done deliberately by those who know how, but also can happen accidentally if you screw up while using the One Power) by the White Tower, an alliance of female Channelers who call themselves 'Aes Sedai'. Civilization is in gradual decline, after two major disasters, the Trolloc Wars and the War of the Hundred Years, which wrecked two periods in which the world had finally started to recover from the end of the Second Age. Nations are slowly shrinking, and wilderness creeps over more and more of the world. And now the seals on the Dark One's prison are beginning to weaken.
It is at this time that the Dragon is reborn as Rand al'Thor, a farmer from the Two Rivers, a rural backwater noted only for producing good tabac (tobacco). He is blissfully unaware of his destiny until an Aes Sedai named Moiraine and her Warder, Lan, show up in the Two Rivers, right as the Shadow's own forces come looking for him. He, his friend Mat (a charming rogue of a boy), his friend Perrin (a blacksmith's apprentice), his sweetheart Egwene (daughter of a tavern keeper), the village Wisdom Nynaeve (more or less the local wise woman and leader of the local women), and a gleeman named Thom Merrilin (a travelling minstrel and player of political games) end up fleeing the Two Rivers with Moiraine and Lan.
As the books progress, Rand comes to learn of his destiny and accepts that he is the Dragon Reborn, becoming a leader of nations (not always with those nations whole-hearted consent). He becomes a potent male channeler and swordsman as well. Perrin becomes a wolfbrother, able to speak with wolves and becomes a lord of sorts, against his will. Mat, also against his will, ends up a great general and leader. Egwene and Nynaeve both end up as Aes Sedai. The White Tower splits in a power struggle and Egwene ends up the leader of one of the factions.
Meanwhile the Darkfriend leaders who were sealed with the Dark One, now known as the Forsaken, have escaped the Bore and now seek to pick up where they left off, endlessly squabbling with each other and waiting for the seals on the Dark One's prison to break completely, each hoping they will be named Nae'blis, the Dark One's viceroy, to lead his forces at Tarmon Gai'don, the battle which will end the Third Age.
There's a LOT more to what's going down than that, but I think that
conveys the basic idea of what's going on in this series.