Just for the record, I have done it all - I have walked with no reservations whatsoever, have booked ahead night by night, and hired a company to make all of my bookings. I have stayed in albergues, small hotels, B&Bs, church pews, and even the Paradores. It's your camino - you do what you want.
The towns we stop in for the night are small. It doesn't matter where you book or sleep - it will be a stone's throw from the other pilgrims, so go ahead and book if you want.
If you do want to book ahead, I am happy to help you, though I'm just going to make you set up a Booking.com account and book all of your accommodations that way.
Booking.com, more than any other accommodation reservation website, is your best bet for making reservations. Click here to make reservations on the Camino.
Everyone should experience an albergue at one point of another. These are large dormitories with a shared bathroom and lots of bunkbeds. They run around $6-$8.00 a night. They are super clean and come with a variety of offerings (some come with dinner, breakfast, etc.). Your guidebooks and apps will detail all the amenities of each albergue.
Small hotels and B&Bs are prolific on the Camino. You'll get your own room and private bathroom. Some have breakfast (usually coffee and toast) which I personally like. When making reservations, make sure you indicate whether you want two beds or one (if you're sharing with someone). And these are European beds, so a "double" bed is the size of our American twin.
Along the trail you will find some opportunities to stay in Paradores hotels which are very expensive, historical sites, along with nice hotels for a lot more money.
You may camp! You are in the countryside and there are lots of opportunities to camp if you so desire. In addition, there are quite a few albergues that will let you sleep in their enclosed yard so you can take advantage of their bathrooms and services.