The origins of the Camino de Santiago goes back one thousand years and it was an important christian pilgrimage route during the middle ages, all walking to seek forgiveness from St James. It is though that the remains of the apostle saint james is buried in the Cathedral of Santiago de Compostela.
In modern times pilgrims walk it for many reasons, not only religious, and to be a pilgrim has changed its meaning. What attracts people to the camino de santiago today, I think, is the mix of adventure, seeing spain and its culture and the camaraderie that builds up over several weeks of walking. Pilgrims that walk come from all over the world and that creates a great environment. Mix that with some good spanish wine and food, and you have the perfect experience.
The first ever guidebook, was written for the camino de santiago and is called the codex calixtinus. The modern day pilgrims use the internet and camino guides to prepare their walk. While on the camino, the need for such a camino guide varies. To find your way, it is not needed. You will have plenty of yellow arrows guiding you along. But it might be handy to have a camino guide to facilitate finding a place to sleep each night, if you choose not to stay in albergues.
The routes have public alberuges in almost every town at the end of each stage. These public alberges charges a low fee and gives you a shower and a place to sleep. This is usually bunk beds in rooms with 10-20 other pilgrims.