The Book of Three by Lloyd Alexander
This is the first book in The Chronicles of Prydain. We meet Taran, an Assistant Pig-Keeper, who wishes to learn the arts of sword-making and fighting instead of his daily chores of looking after the pig Hen-Wen and assisting with daily chores such as hoeing the garden and feeding the animals. Taran has dreams of being a great hero, but one day when Hen-Wen runs away and he chases after her, he finds that being out in the world on his own is not all that he thought. He meets a rough-looking, ragged man and is surprised to learn that this man is Gwydion, a great war hero. In his adventures as he tries to recover Hen-Wen, Taran meets the Horned King, a part man part beast named Gurgi, Eilonwy, dwarfs, and many other strange and mysterious creatures. He knows that he must return home to Caer Dallben to warn them of the approach of warriors from Annuvin. If you enjoy fantasy and adventure, this is a book for you. There are 4 other books in The Chronicles of Prydain.