First off, there's not a lot of difference between volunteer and full-time, other then the hours you work and the pay scale.
Second is that probably still the best book on the subject is REPORT FROM ENGINE COMPANY 82 by Dennis Smith. But there's tons of material out there.
Different departments have different requirements, and each state has slightly different requirements as well. For many of the certifications, you do it once and you're done. However, for firefighter, there are usually a couple of levels, and then some command stuff that most firefighters take. If you're an EMT, you have to take something like 48 hours training every two years and take a test.
Then there are a bunch of esoteric certifications, like Haz-Mat, radioactive, farm rescue, brush fire, water rescue, and on and on and on. Some of these certifications last forever, others need to be renewed.
Most departments will run some of these classes, while others might be more regional. You'll probably do some of this on your own time.
Typical schedule for a firefighter might be 24 hours on, 48 off. During their 24 hours on, from 8 AM to 4 PM for instance, would be official time, where you do 2 hours cleaning the station, 2 hours checking the truck's equipment, 2 hours training, and 2 hours eating, bathroom, and things like that.
But virtually every day you're going to be doing some training, run by the truck's officer. That's because you've got to have these automatic responses, ranging from knowing exactly where Smith Street is, to using an SCBA. You can't think about this stuff in an emergency.
Firefighters tend to be an unusual personality type. For instance, I've never lost a cellar hole or had a patient die in the rescue. They're either dead when I get there, or the doctor kills them off. Firefighters know that everything resolves.
Many firefighters, as well as their fire department job, work part time.
Best of luck,
Jim Clark-Dawe