The Magicians Nephew

 This is the first book.  It tells about the creation of Narnia by Aslan, The Great Lion.  You learn why most of the things that happen in the rest of the books by reading this one.

The Lion, the Witch and the Wardrobe

 Many years have passed since the creation of Narnia.  Jadis, the White Witch has taken over and has put Narnia under an eternal winter.  Peter, Susan, Edmund, and Lucy are called by Aslan come to put an end to the White Witch and her evil .

The Horse and His Boy

 This takes place while Peter, Susan, Edmund, and Lucy are high kings and queens in Narnia.  A boy named Shasta and a horse named Bree escape thier slavery and save Narnia from war with the Calormenes.

Prince Caspian

 Much time has passed since the golden years of Narnia.  Now the Telmarines own it under King Miraz.  All the talking and mythological beasts are in hiding.  However, all the high kings of the ancient days have come back to restore Narnia with Aslan.

The Voyage of the Dawn Treader

 This story takes place a little while after Prince Caspian.  Edmund, Lucy, and Eustace are all sent into Narnia.  They come to help Caspian find seven lords that King Miraz sent away.  They also find Aslans country and meet Aslan.

The Silver Chair

 In this story, Jill and Eustace are sent into Narnia by Aslan.  They must save King Rilian, the son of King Caspian.  King Rilian has been caught by the Green Witch, a descendant of the White witch.  Jill and Eustace save him and bring him out the power of the Green Witch.

The Last Battle

 This is the story of the end of of Narnia and the beginning of the new one.  A false Aslan roams the land  guided by Shift.  Shift has control of Narnia and  Colormene as well.  The Colormenes march into Narnia and King Tirian, the last king finds his way into a mysterious stable while in Battle.  In it, he finds Tash, the God of the Colormenes.  The seven friends of Narnia defeat Tash and Save the King.  After that, they all find that they're in a new Narnia that is forever in peace.