Reddit mentions of The Path of Druidry: Walking the Ancient Green Way

Welcome to the sub, DM mentioned the ADF but I don't think they'd be the organization for you if you're more on the athiest/agnostic spectrum as the ADF takes a more religious, polytheistic approach. I'd look into the Order of Bards, Ovates, and Druids (OBOD) and the Ancient Order of Druids in America (AODA) if you're looking into an organization to join. Many druids are solitary though and never join an organization, though there are advantages to doing so. They're a good source of guidance.

Most people start by reading books though, I'd also suggest reading the first two links in the side bar. One is a sort of 'summary' of the modern druid movement, the second is a comprehensive history of how it came about.

Some good 'starter' books are:

The Path of Druidry by Penny Billington

The Druidry Handbook by John Michael Greer

Druidry and Meditation by Nimue Brown

A Brief History of the Druids by Peter Berresford Ellis

Several of the above authors also have blogs that a lot of people read and follow.

I tend to suggest the above because it covers a few different approaches to things, I feel like it's important as druids today to understand the past and where we get our influence from, which A Brief History of the Druids provides, both the Druidry Handbook and the Path of Druidry offer a good introduction to modern druidry, and Druidry and Meditation provides some instruction and guidance on meditation, which a lot of druids practice, and also I think does a good job of displaying the mentality and energy of many modern druids.

The thing about modern druidry though is there really isn't a right or wrong way as long as you adhere to the very basic beliefs of respecting all life (this doesn't mean necessarily being a pacifistic) and revering nature. You can be an atheist, a pantheist, a monotheist, a polytheist, Christian, Pagan, Buddhist, whatever. Which means it can be a little intimidating to new people, since you're kind of just tossed into this big forest and told to figure out your own way through it, but you learn a lot.

I think it's also good to note that modern druidry is not an attempt at recreation, if you read a Brief History of the Druids, you'll figure out that we actually know very little about the ancient druids, so it'd be very difficult to recreate their order.

Hey there! I have some recommendations, and I'm sure others do as well, but if you're looking for introductory-style books, here you go!

• The Path of Druidry: Walking the Ancient Green Way by Penny Billington (Amazon link)
  
• The Druidry Handbook by John Michael Greer (Amazon link)
  
  I'd also recommend OBOD and ADF's websites; they're chock-full of information! And of course, feel free to ask here if you have any questions.

Some good online resources:
OBODs Druidcast
Ian Corrigan, an Archdruid Emeritus of ADF, has a cool video series he is doing called Under the Oak

And here are a bunch of books:
The Druidry Handbook by John Michael Greer
The Druid Way by Phillip Carr-Gomm
The Mysteeries of Druidry by Brendan Myers
Bonewits's Essential Guide to Druidism by Isaac Bonewits
Principles of Druidry by Emma Restall Orr
The Solitary Druid by Robert Ellison
and The Path of Druidry by Penny Billington (this one is a personal favourite that I recommend to nearly anyone who asks this sort of question).

Hope that helps some. :-)