Reddit mentions of The Druidry Handbook: Spiritual Practice Rooted in the Living Earth

There are not actually very many articles about modern druids, there are organization websites like the one for the Order of Bards, Ovates, and Druids and A Druid Fellowship

And there are several good blogs like John Beckett on Patheos, Damh the Bard (a very well known and influential figure in modern Druidry), and the Archdruid Report by John Michael Greer, the Grand Archdruid of the Ancient Order of Druids in America

Thing to remember is that there are three main approaches to modern Druidry, one is as a religion, people who worship gods, perform rituals, so on, those that approach it as a spirituality and therefor don't hold gods or ritual with as much importance and focus more on themselves than outside forces, and then those who approach it as a philosophy, these people might not even be theistic at all, and tend to focus on the physical world rather than the spiritual one. There are people fall in between of course but that's the basic gist of it. You're going to have to figure out where you fall in that before you have a better idea as to what kind of information and guidance you're looking for.

A few books you could look at are:

The Path of Druidry

The Druidry Handbook

Bonewits's Essential Guide to Druidism

A Brief History of the Druids

It's important to try and read something like that last book especially to give you some sort of context as to how and why modern Druidry came to be. It isn't an ancient religion, we have no ties to the ancient Druids, and very little knowledge about them at all. So to avoid looking foolish, I'd suggest definitely reading something about the history of the Celts and the Druids, and the modern movement.

Also, spiritual ecology books are a good supplement, Druidry is focused on nature so of course learning about nature, ecology, biology, and such is only going to help you. My two favorites are Spiritual Ecology: The Cry of the Earth and Mystery Teachings from the Living Earth: An Introduction to Spiritual Ecology

I'd say in terms of nature-oriented Pagan "faiths" you've got Druidry/Druidism, Wicca, Traditional Witchcraft, and Heathenry (i.e., Asatru, Vanatru, Rokkatru, Northern Tradition, what have you) immediately jumping to mind, but those are also the ones I'm most familiar with. There's a ton of other ones, and they may or may not be as nature oriented as those are; I'm sure someone else'll bring them up in time.

Druidry's probably the most nature oriented of the lot but depending on the practitioner and what they're doing members of the other ones can be just as nature centered in their practice. A good book for that is The Druidry Handbook by John Michael Greer, which is where I'd start (and where I started with Paganism, to be honest, though I'm Heathen now).

John Beckett, another druid, wrote The Path of Paganism recently; I haven't finished going through it but it looks like an excellent introductory text for anyone who doesn't know much to anyone who wants to explore new areas of Paganism. Actually now that I'm thinking of it, that's where I'd start, and I'd pivot to the Druidry Handbook if Druidry seemed appropriate afterwards.

Look into those, maybe find intro texts to the other subsets that interest you, talk to people, and if you want you can message me and I'll help as I'm able to.

You might try reading The Druid Handbook https://www.amazon.com/dp/B007L4SUPU/

The Sphere of Protection is described thoroughly in John Michael Greer's The Druid Magic Handbook. The Kindle version should be easy enough to keep private. It's also available on Scribd if you subscribe to it.

It can be used on its own, but is also a companion book to JMG's The Druidry Handbook, which is suitable to someone practicing alone but is also the AODA's primary text.

There are plenty of other druid organizations and druidry authors, with different styles, but I would suggest the books mentioned above because I think highly of JMG as an author, and because, of the other two most prominent druid organizations, ADF is very much about engaging Druidry as a polytheistic pagan religion and might not suit you, and OBOD mails you course materials that are 1) kind of expensive for a college student, and 2) difficult to keep private since you're getting physical materials mailed to you.