Standard tuning is: First four string pairs, from thickest to thinnest are EE AA DD GG but each pair is tuned an octave apart. Last two pairs are BB EE but each pairs is in the same octave -- same pitch. Yeah, I did try to tune the last pairs an octave apart too...they broke real good :-)

You, of course, can tune 'em all however you like. My favourite alternate tuning is DD AA DD GG AA DD. Stan Rogers uses this tuning in Witch of the Westmorland, among other songs, and it sounds so crisp, that he must have retuned after he stuck his capo on the fifth fret.