I have read Portrait at least a couple of times before. Joyce tried publishing it under the name Stephen Hero, rewrote it, and finally succeeded in publishing it in 1916.
This book is considered to be at least semi-autobiographical. No matter, it is an excellent work of what I'll call interior fiction, that is, it is a story that happens mostly within the mind of its central character. This type of fiction is not uncommon from modern writers, but Joyce was one of the first to place the conflict and resolution of a novel within the consciousness or mind of a character, rather than centering upon actions and conflicts between people, places, and things in the visible world. This type of writing is also known as stream of consciousness, and William Faulkner explored the technique extensively in his work.
Portrait is not an easily read, or "accessible" book, but it is far less cryptic or obscure than Joyce's later works, Ulysses, and Finnegan's Wake. It begins with its principal character's babyhood. Stephen Dedalus is hearing his father tell him a children's story:
Once upon a time and a very good time it was there was a moocow coming down along the road and this moocow that was coming down along the road met a nicens little boy named baby tuckoo...From inside young Dedalus' mind we grow up with him. He goes away to school at Clongowes, but this is cut short by the financial problems that plague his father, and grow worse throughout the story.
When Dedalus and his family move to Dublin (at the beginning the family lives in Blackrock), they have come far down economically. Politics are constantly in the background, and there are strong hints that Dedalus' father's troubles are at least partly political.
Dedalus next attends a Jesuit school. Here he wins a prize for acting in a school play, and is temporarily rather wealthy. He squanders his money rapidly, buying food and gifts for his family, and begins to sample the prostitutes of Dublin. Catholic religious guilt soon overtakes him: There are thousands of words devoted to the brilliant and horrifying descriptions of Hell provided to the students by priests during a "retreat" at school in honor of St. Francis Xavier.
--We are assembled here today, my dear little brothers in Christ, for one brief moment far away from the busy bustle of the outer world to celebrate and to honour one of the greatest of saints, the apostle of the Indies, the patron saint also of your college, saint Francis Xavier. Year after year, for much longer than any of you, my dear little boys, can remember or than I can remember, the boys of this college have met in this very chapel to make their annual retreat
before the feast day of their patron saint....
...The preacher's voice sank. He paused, joined his palms for an instant, parted them. Then he resumed:--Now let us try for a moment to realize, as far as we can, the nature of that abode of the damned which the justice of an offended God has called into existence for the eternal punishment of sinners. Hell is a strait and dark and foul-smelling prison, an abode of demons and lost souls, filled with fire and smoke. The straitness of this prison house is expressly designed by God to punish those who refused to be bound by His laws. In earthly prisons the poor captive has at least some liberty of movement, were it only within the four walls of his cell or in the gloomy yard of his prison. Not so in hell. There, by reason of the great number of the damned, the prisoners are heaped together in their awful prison, the walls of which are said to be four thousand miles thick: and the damned are so utterly bound and helpless that, as a blessed saint, saint Anselm, writes in his book on similitudes, they are not even able to remove from the eye a worm that gnaws it.Nice stuff.
As the story progresses, we see Dedalus become more and more disillusioned with the Catholic religion that controls his country and countrymen. This causes him much conflict with those around him, not the least of whom is his mother.
The story ends with journal entries. Here is one of them:
APRIL 10. Faintly, under the heavy night, through the silence of the city which has turned from dreams to dreamless sleep as a weary lover whom no caresses move, the sound of hoofs upon the road. Not so faintly now as they come near the bridge; and in a moment, as they pass the darkened windows, the silence is cloven by alarm as by an arrow. They are heard now far away, hoofs that shine amid the heavy night as gems, hurrying beyond the sleeping fields to what journey's end--what heart? --bearing what tidings?
Dedalus will be leaving Dublin, leaving Ireland, even as Joyce did, but it will never leave him, as it never left Joyce. In this book Joyce began some of the techniques that he would develop in Ulysses and Finnegan's Wake, and continued to work on expressing the peculiar relationship with Ireland and Irish culture that characterized his life's work and literary legacy.
Some more information:
Wikipedia Entry for James Joyce: http://en.wikipedia.org/wiki/James_Joyce
Guardian article about Nora, a film about Nora Joyce.