What is the North Star called in Narnia?  

The North-Star in Narnia is called the Spear-Head: it is brighter than our Pole Star.

How did Tirian find his directions as they travel through the night in the dark?  

Tirian found his directions according to “tie a starry night”. They could go straight towards the Spear-Head. But then they were missing in the dense thicket. But Jill could work out the directs from other stars,  Tirian put her in front of them as a guide.

What does the noise of the far-off drumbeat indicate? 

The army of dwarfs were coming near to meet them. as well as enemies  - armed Calormenes came steadily near them.

What does Lucy find in the stable? 

The false Aslan, the donkey-who pretended the Aslan